What value do you see in studying theology in concerns to Christianity?

[John 6IX Breezy]

Yes, absolutely! 

It's a big baggy term of family resemblance (in Wittgenstein's sense), under which individual Christians may have almost nothing in common. 

I find myself in the odd position of defending them, saying over and over -- no, not all of them believe that, that is not an intrinsic part...

I think that, because it is a big bag, its easy to look to the fringes and assume you are looking at the whole of Christianity. Even entire denominations tend to have strong main points that define their church, but also weaker sideline beliefs that just stray along or emerge culturally (probably cause we all need to have an opinion on everything) but aren't essential. I think these sort of fringe beliefs emerge whenever you take individuals and try to form a collective group. You'll find random fringe beliefs in political parties, etc. Given that that's the case, its easy to pick all the fringe beliefs from every church and construct a picture of Christianity that is less than accurate. So my point is, whenever you look at a group, particularly religions, I think its necessary for the observer to seek it out in its most reasonable and persuasive form.

Addendum: I do think most average Christians have a neutral and reasonable view on God as loving but just, etc. And for those on the fringe that do believe in the angry man in the sky thats all punishment and no love, there are also those on the opposite end that believe in the happy hippie in the sky thats all love, no hell, everyone's saved, etc.