We've talked about it elsewhere, but my major 180 was on the ethics of consuming animal products. I grew up hunting and fishing for a non-trivial portion of my diet, but have come to see that and almost all animal farming practices as unethical.

I probably haven't done a full 180 on religion, because I'm still not religious myself, but I've done something like a 170 on it. In college I was a militant agnostic and read a lot of the "New Atheist" books. However, I've come to see religion as being very important in maintaining the social fabric in a healthy culture.

Similarly, while I've always hated the government, I've done a 170 on it: going from being a constitutionalist libertarian to a strict voluntaryist.