Which requires a bigger ego, believing that you personally have been singled out and chosen by God for some special purpose, or believing that your entire ethnic group (race, family, whatever) has been singled out by God for some special purpose? Believing you're chosen by God may be personally fulfilling, but believing you belong to an entire group that's chosen by God means you're part of a larger, divinely-ordained movement and group. Either way, you are raised up out of the masses.
Unfortunately, there are always others out there who try to make the same claim: there are other individuals who insist that God has actually chosen them for some other task and there are groups of people who insist that they are God's chosen people. Just how many "chosen people" can there be? Given how mutually incompatible their claims are, they can't all be chosen. Even worse, their basis for claiming to be chosen often rests on ancient documents created by nomads who had barely a fraction of the knowledge of the world we have now. Why are such claims treated as credible, except that they tell people what they want to hear?
People who think they are somehow specially chosen by God sometimes exhibit a contempt for the standards of behavior expected from the non-chosen people. This isn't hard to understand because if you really have been singled out by God for a special job, then why should you let the mundane rules that apply to others create barriers for you? God has a job or goal for you and you shouldn't let anything stand in your way, should you?
Although every ill caused by religion can also be caused by secular ideologies, this is one of the factors which separates religions from secular ideologies and makes the harm they cause much worse. No secular ideology encourages the belief that one should be committed to a task that is approved of or desired by gods. This is a problem because it makes compromise and change far more difficult — if you sincerely believe in a god and sincerely believe that it has given you a job, then compromise means compromising on this god's wishes and that's just not acceptable. Even the most dogmatic secular ideology allows a bit more room for compromise and none encourage the idea that any gods have singled you out as special.