I wasn't aware that anyone had blamed christians as a whole (as a group of people) for the crusades.
Thing is, ideas/beliefs can be blamed for events just as much as people can. In fact it is pretty much how we assign blame. Mr Smith committed such and such an atrocity because he thought that such and such a thing justified it. Mr Smith is wrong and the belief he used to justify the action is wrong.
Lets take your small government example (mostly because the christian/crusades one would lead to yet another biblical interpretation argument, though I'll go there if you want). Lets say we have an idea and that idea is expressed as:
- Government is an organisation that by it's nature often restricts the freedoms of citizens in ways that are harmful to society. Government should remain small and be restricted to only acting in X, Y or Z spheres of influence. Citizens have a civic duty to restrict the powers of government to only the essential things that only government can do.
(I'm not saying this is the actual position of anyone btw, just making an example in an effort to crystallise my point)
Now, some nutbag picks up this idea, and blows up a government building killing hundreds of government employees. Is that my fault for having the principle I described above? No of course not. Can we look at the stated belief/idea there vs the action and see if the action is consistent with the belief/idea? Well the bomber, at least in the short term, has reduced the size of the government and restricted the influence it has. Any government actions that were being done through that office by those employees will be heavily disrupted.
Now we could say "but that's not what we meant, we meant people should do this through the democratic process and by non-violent means" but that wasn't in the way we summarily described the idea. And the more we clarify the idea the more other people will clarfiy the idea differently, and you go from a basic well-defined principle or two about small government which a large group of people agree to to a big definitonally-fuzzy thing that some people agree with some bits of and others agree with other bits of and there is nobody left with the ultimate authority to say "this is what the idea is", nobody to tell the nutbag bomber that he definitively has the idea wrong by interpetting it in a certain way.
The authority bit is important, because rightly or wrongly we put people into authority, or at least of influence, on the basis that they represent the ideas. So for small government see Tea Party, the most established small government political movement, and their spokesmen. We look at what their spokesmen have said and we see if it is consistent with what the nutbag bomber says:
http://msteaparty.ning.com/?xg_source=msg_mes_network(edit - link is dead - possibly the staement is removed - but google "MSTP Statement on Obamacare" for it being reliably reproduced by a lot of different sources - trying to find a live link for it now)
(note the official tea party web address, click at your own risk and realiise that I am not straw-manning - emphasis added by me)
When a gang of criminals subvert legitimate government offices and seize all power to themselves without the real consent of the governed their every act and edict is of itself illegal and is outside the bounds of the Rule of Law. In such cases submission is treason. Treason against the Constitution and the valid legitimate government of the nation to which we have pledged our allegiance for years. To resist by all means that are right in the eyes of God is not rebellion or insurrection, it is patriotic resistance to invasion.
Here we have the tea party saying that violent resistance is justified and indeed patriotic. And this is why tea party gets associated with violent anti-government actions. Because they themselves say that such actions are justified.
We can do exactly the same thing with the crusades and papal authority. We can do exactly the same thing with the Nazis and Lutheran anti-semitic protestantism. Nobody is blaming christians for the crusade, but we are justified in blaming christianity. Nobody is blaming Lutherans for the holocaust, but we are justified in blaming lutheran anti-semitism. Nobody is blaming tea party supporters for the violent nutbag, but we are justified in pointing to tea party philosophy...