What's the harm? There cannot be many who have engaged in debate about 'weird beliefs' who has not had this question thrown at them!
It can seem like a very pertinent question and it can be surprisingly difficult to answer; particularly when you're dealing with a single case like someone's mother who believes in angels: "If she believes and it brings her comfort, what's the harm?"
The problem with this argument is that it's based on the Hasty Generalisation fallacy (the fallacy of insufficient sample), and the False Dichotomy fallacy (where only two alternatives are considered). The implication being that if one person's mother believes something weird and hasn't been harmed by it then this sort of belief is therefore universally harmless. This position is further confounded by the fact that the idea of 'bringing comfort' is an Appeal to Emotion so trying to oppose or take that belief away makes the person look somewhat mean and cold-hearted.
It is probably better to acknowledge that for most people, most of the time, that holding weird or irrational beliefs will not result in harm. In fact, people hold these beliefs because they get some benefit from them. Belief in the afterlife and that mediums can pass messages from the dead can give people the comfort of believing (they'd claim knowing) that their loved ones haven't really died, or adopting a 'holistic lifestyle' of only eating organic food and only using alternative medicine can give people a feeling of empowerment by taking control of their health (the 'illusion of control'), promoting well-being and preventing disease, for example.
However, such beliefs do pose the threat of harm. Someone who treats their family with homeopathic remedies rather than conventional medicine will not be harming anyone most of the time as most illnesses and diseases are fought off by the immune system anyway; but if a family member actually develops something serious and it is treated with homeopathic remedies, that is when the potential for harm occurs.
So what we have here is not an absolute position where we can say that everyone who holds weird beliefs is going to be harmed by them, but a one where we can say that people who hold and trust in unaccepted and even disproved ideas are putting themselves at an increased risk of being harmed. Holding irrational beliefs is a risk factor for harm, not an absolute.
Irrational beliefs, and actions based upon them, are more likely to cause harm to people in times of crisis rather than in their day-to-day lives.
How harm can occur
The "what's the harm?" arguments tend to be used with regard to single cases with a certain context - as illustrated in the introduction; however, harm from irrational beliefs can occur in many different ways depending on who holds them and the position they hold in society. Some ways in which harm can arise from irrational beliefs include:
- Economic harm
This can occur to individuals, businesses, government agencies, institutions, etc. Spending hours on the phone to 'gifted psychics' can prove extremely costly to the individual; lending huge sums of money to people who can't afford to pay it back in the chase for more profit can prove extremely costly to banks, the government, and ultimately the taxpayer (as we have recently found to our cost!); spending money to 'invest' in an MLM business in the hope of making it rich.... one day. - Direct harm
Direct harm occurs as a direct consequence of an action: Suffering a stroke after a chiropractic neck manipulation; being poisoned or killed by the unknown compounds in a herbal remedy; severely malnourished children due to being fed a strict vegan diet by their parents; a woman needlessly dying in childbirth because her religion has interpreted scripture so that blood transfusions are not allowed. - Indirect harm
Indirect harm occurs as a consequence of previous action or due to the beliefs and actions of others: Children dying through needless treatments for autism because the parents believe that it was caused by heavy metals in a vaccine despite the evidence against this; physical/emotional harm caused by avoiding proper medical care because of the belief in alternative medicine; children being harmed or killed by preventable diseases because their parents believe the anti-vaccination propaganda. - Psychological harm
Caused by psychological investment in irrational concepts: False hope being given by 'psychic detectives' who involve themselves with murder and missing persons cases; distrusting things like medicine/science/institutions/etc. through conspiracy theories; irrational fears of things such as Mercury in fillings, Aspartame in food, or fluoride in water; stress and anxiety caused through the belief in curses and spells, possession by demons, etc. - Social harm
This can manifest itself by things such as: poor public policy (using lie detectors to monitor paedophiles); wasting resources (using taxpayers' money to fund homeopathic hospitals); preventing scientific research and advances because of religious arguments; making major decisions without basing them on evidence or in spite of the evidence - e.g. going to war based on the belief that the enemy possesses weapons of mass destruction.
Evidence
Although we often hear of such harm and it makes intuitive sense that believing in things that aren't true would have the potential for harm, it is surprisingly difficult to quantify this harm. Of course that doesn't mean it isn't occurring, it's just that no one is monitoring and measuring it systematically.
It is known and accepted by many that in some cases people are psychologically harmed by their visits to mediums in the quest to contact a dead loved one. This can result in harm caused by things the medium comes out with in one reading or it can be a case of the person developing what's known as 'psychic dependency' (where they become 'addicted' to mediums and 'spirit contact' and get trapped in the grieving process) - however, there are no official figures as to the prevalence of this type of harm.
Fortunately, there is a website that is documenting cases of harm that have been reported in the media. See: What's the Harm?
These cases are only the ones that have made the media, and so will be a gross under-representation of the true figures, but at least they do provide an evidence trail as the stories can be verified, and there's a section providing scientific evidence too.
Conclusion
The case for harm caused by irrational or 'weird' beliefs is probably a one that is overstated much of the time. For most people, most of the time, their beliefs will not cause them any harm and probably provide benefits; which is the likely reason they persist.
However, this does not mean that such beliefs are without their consequences. The potential for the different types of harm outlined above increase when people rely on them most (times of crisis) or when people who have influence hold them. There is no reason why someone who holds weird beliefs or an irrational world-view cannot make high office!
Arguing with someone asking "what's the harm?" can be difficult, as whether a belief (or action based upon it) causes harm is context dependent.
Telling someone that their granny is at risk of harm because she attends a spiritualist church to get messages from her late husband is really not making a strong case (in fact it would make the opponent look foolish); but when it's a government official who believes in homeopathy and is in a position to allocate public money, then the case for harm is clear cut - in this instance spending money on homeopathy instead of proper medical care could result in indirect harm (patients losing out on real treatment because the money was spent in a homeopathic hospital instead, for example).
So yes, irrational beliefs can and do lead to harm. It is also frequently quite difficult to get this point across in a debate, as the context is often not appropriate; for example, single-case scenarios considered at one point in time only. To understand the potential for harm, we need to assess the bigger picture; for that is the correct context in which to appreciate this issue.