Eh, if the things labeled christian diverges wildly from what you believe, what you believe probably isn't christian, though you likely shanghai'd the name. Various presbyterian denominations do indeed vary wildly, but they either share certain core concepts nevertheless or they're lying about their beliefs in one way or another by claiming the name. You do want to judge people individually, but at the same time you don't get to claim association with something and then avoid scrutiny for what your claimed group is doing. You can't claim to not be anti-LGBT and be voting republican, ferex (though you may be able to be voting conservative, so long as whatever party or individual you're voting for isn't voting lockstep with the GOP). However strongly you say the former, the latter puts it to lie. With some sorts of association, certain things stop being assumption, and denial by the person associating starts being a lie, regardless of what the individual has told others, or even themself, what they believe.
Religion's a fair bit more muddy than most things political, though. Funding and political support and whatnot paints you, but by and large much of what's related to religion functionally doesn't matter outside your head, holy texts can and have been twisted to invalidate any particular belief associated with them, and so many bloody people claim the top level names they're effectively meaningless -- muslim, ferex, may mean you see the qur'an as a holy text and claim belief in a specific holy figure or two, but how you or your denomination interpret the former or view the latter is pretty much entirely up in the air.
You still have metaphorical problems (so far as wanting to claim you approach others in a sort of tabula rasa state) when you're claiming a specific denomination -- "christian" says basically jack all about your beliefs, but "baptist" or whatev' says quite a bit more -- or talking about a specific region, but it's a lot less necessarily clear, and there's a lot more wiggle room, with the occasional exception. LRA says a hell of a lot more than, say, catholic, heh. Philosophy or ideology is about in the same spot, really, though those those tend to not splinter into a dozen things fighting over the same name quite so regularly.
There's also a fair bit of difference between talking about an individual member of a group and the group itself. Lot less of the things stated about the latter can be claimed to be assumptions. A criticism of a group you associate isn't necessarily a criticism of you, after all. Unless you're displaying or supporting whatever is being criticized, anyway.
... do wish the bloody denominations would name themselves more clearly, though. Know why they do it (wanting to claim authority over a certain title, since new denominations tend to form due to schisms within a particular denomination), but good gods does it make things more annoying.