Why is it that people who have such a problem with security cameras in public, seem to extrapolate to unrelated things?
Serious questions. Considering you feel no expectation of privacy in public, would you...
1. accept mandatory personal ID & tracking for every site you visit on the internet (which is arguably "public space")?
No. The internet isn't public. It is the internet, wherein the descriptor 'public' only applies to posts you actually make, or material you provide which anyone has access to. Besides, the fact that it would easily circumvented kind of suggests it isn't the kind of public space we are talking about. You are suggesting something like mandatory wire tapping of phone lines. That kind of thing certainly isn't ok, is it?
2. accept mandatory wearing of armbands in public, identifying your religion, sexual orientation, political affiliation and income?
What does this have to do with CCTV cameras? Even if the government was able to obtain this information (which, in almost every case, can be obtained by other means such as census data, public registries, and so on). But let me put this to you: if you sit down in a public park and start to pray, do you think you have an expectation that no one is allowed to know your religion? Or if you drive around in an expensive sports car, do you thin you have the right for people not to know how much you make?
3. answer questions about your public activities (clubs you go to, items you buy, web sites you visit) when you apply for a job?
Again, what does applying for a job have to do with the government possibly storing data about persons based on what they do in public? If you are going to argue that 'evil corporations are going to obtain this information', isn't that a problem with your government and not with the CCTV cameras? Also, doesn't google et al already have most of this information already, based on your searching habits?
4. be ok with all your public activity being brought up in court, used as "character evidence" when, say, applying for adoption, divorce or fighting for custody of your child?
Yes. I'm fine with this. Why? I did something in public. I shouldn't expect people didn't see me. Say I'm going through a divorce. My wife brings in a video of me physically abusing her in a car park. I certainly think that evidence should be used against me. Why would you expect anything else?
Or do you now understand that the expectation of privacy in public is, in fact, a cornerstone of democracy and law?
No. I think the ability to select your government by popular vote is the cornerstone of democracy, and said government and other officials following and adhering to the law, as written, is the cornerstone of law. Public places never have been, and never will be, private in any meaning of the word. Where is private? Your own head. Your own house. Etc.