PGs thesis seems to boil down to this: If you believe in something strongly enough, it will cause you to want to defend it and you may compromise your rationality and civility as a result. For which reason we should believe in as little as possible and be as non-committal in our beliefs.
I'm not sure that this is an ethically tenable position: shallowness extolled as a virtue. It's true, people who don't believe in anything don't argue about religion and politics, they fight over fashion and celebrities. I'd prefer people to have strong, well-formed opinions that they are ready to defend, even against me, to people with no opinion at all.
No, that wasn't what I was saying. There is a difference between having strong opinions and considering something part of your identity. You can discard an opinion if you get sufficient evidence to the contrary. It's harder to discard your identity.
Moreover, identifying as something doesn't necessarily take the form of having any specific opinions. E.g. identifying as southern (in the US) may cause you to have certain opinions, but it doesn't consist of having them. Someone who wasn't southern but happened to have the same opinions wouldn't thereby identify as southern.
I believe that if you hold certain opinions, strongly enough, they change who you are. If you truly believe in the value of altruism (for example) you can't help but become more altruistic. If you don't let your opinions change who you are, it's a fair question to ask, whether you even hold those opinions.
Granted, I understand that you are more concerned with making sure people keep a certain emotional distance from their opinions, so that they can maintain a level of objectivity, but I'm not sure that that is always feasible, without adopting a certain kind of passivity or relativism.
You can believe in or participate in something without having it form a significant part of your identity. Usually we say something like that is a "preference" or "opinion", but the difference in name is only a an indicator that it is less coupled to our identity than that it is a distinctly different kind of thing.
It's true, people who don't believe in anything don't argue about religion and politics, they fight over fashion and celebrities.
This is an excessive generalization, and a false dichotomy. The people who argue over fashion or celebrity are those who have incorporated it into their identity. Those subjects are distinct from religion in politics by a matter of degree, not category.
A typical person responds very differently to having their religion criticized than they do having their favorite flavor of ice cream criticized, even though objectively speaking they are both just preferences among a wide number of choices. It isn't even necessarily true that they've given more thought to the former than the latter, only that they identify with that preference much more closely--and criticism of it feels that much more like criticism of the individual.
I'm not sure that this is an ethically tenable position: shallowness extolled as a virtue. It's true, people who don't believe in anything don't argue about religion and politics, they fight over fashion and celebrities. I'd prefer people to have strong, well-formed opinions that they are ready to defend, even against me, to people with no opinion at all.