It is not hard to say when someone has had too much too drink -- they manifest being drunk.  However, drinking can be bad even without intoxication, such as when one is going to drive.

I have a chronic liver condition known as chronic hepatitis B.  It doesn't go away and as far as tests tell us is just sitting there doing me no harm.  However, were I to have a few drinks, the liver enzyme tests would quickly go abnormal.  The conclusion is that people who have this liver condition must not drink at all.  The same applies to all sorts of people with all sorts of health issues.  Alcohol exacerbates a lot of underlying problems.

That makes one wonder whether for most people the negatives might outweigh the positives, even in very small amounts.  It is more and more beginning to seem that that may be the case.

How far is it fair for me to carry this analogy forward with the pluses and minuses of religion?  As with alcohol, a dose of religion can serve to lower one's blood pressure and make one feel better and more sociable.  Still there is a price -- unnoticed but that regardless must be paid.  There is a similar price with belief -- not just religious belief.  Beliefs are an instinctive way of shortcutting rationality, derived from natural selection and basically animal in nature, and in a world dependent on reason, they do insidious and hidden harm.

Cats have a wonderful set of survival instincts, but in a rational city they are in grave peril depending on instincts and need human protection.

We should avoid beliefs as we should avoid intoxicants, and instead try as much as possible to rely strictly on opinions we have good reasons to accept but can modify or abandon given good rational grounds for doing so, and without any institutional or emotional or traditional grasping.