bigotry is a word used to describe someone who doesn't share your opinion, because saying a set of people are good is every bit as generalising as saying they are bad.

Not so. Hatred of and/or attempts to deny the normal benefits of society to a person solely because they are a member of a specific group is bigotry. Calling a person who does these things a bigot is not bigotry. It's not at all about who agrees with who. Being intolerant of intolerance is not an oxymoron.

I agree that calling a group of people good is a form of bigotry -- making assumptions about individuals because of their membership in a group they didn't choose is pretty much the same no matter which way you view that group. The important difference, of course, is whether these beliefs cause someone to do harm or to do good.

The prevailing laws or majority opinion of a populace can be as bigoted as an individual. The United States, right now, is institutionally bigoted against gay people. In the past, this institutional bigotry included women and people of color. There is still LOTS of bigotry against women and non-whites, but at least it is less a matter of law and more a matter of individuals.

It can be very easy to fall into bigotry. It often requires a conscious decision to not do so. When I was young in the late 60s and early 70s, most of the young people I knew always referred to police officers as pigs. Since these were people who prided themselves on open-mindedness and peace and love, they didn't like it when I called their attention to their apparent bigotry. During the push for the Equal Rights Amendment, I always wore an ERA button. This caused lots of other guys, without seeming to think about it all, to display bigotry toward me. There were, at that time, also lots of "feminists" who were adamantly anti-man (even guys wearing ERA buttons!). They also didn't like being told they were acting just like the men they hated. Actually, I once told a woman that I'd rather hear sexism from and ignorant middle-aged man than from a feminist, in that the feminist is supposed to know better. But the point is that lots of people who are otherwise normal, loving folks for some reason find it easy to take on the attitudes of the people around them. It is easier and safer to be share the local majority mindset. I don't consider that an excuse, but it is understandable.