You can easily model beliefs and work out if they're likely to have good or bad results. They could theoretically have a variety of infinite impacts, but most probably have a fairly small and limited effect. Humans have lots of beliefs, they can't all have a major impact.

For the catastrophic consequences issue, have you read this?

http://lesswrong.com/lw/ase/schelling_fences_on_slippery_slopes/

The slippery slope issue of potentially catastrophic consequences from a model can be limited by establishing arbitrary lines before hand that you refuse to cross. Whether you should sacrifice your beliefs, like with Gandhi, depends on what the value given for said sacrifice is, how valuable your sacrifice is to your models, and what the likelihood of catastrophic failure is. You can swear an oath not to cross those lines, give valuable possessions to people to destroy if you cross those lines so you can heavily limit the chance of catastrophic failure.

Allowing your beliefs to change for any reason other than to better reflect the world, only serves to make you worse at knowing how best to deal with the world.

Yeah, your success rate drops, but your ability to socialize can rise since irrational beliefs are how many think. If your irrational beliefs are of low importance, not likely to cause major issues, and unlikely to cause catastrophic failure they could be helpful.