It can be used, but you want it in situations that can be more homogeonized. The way different cultures view black markets for goods can cause wildly different results from banning said goods. I stick to the hard-line correlation does not prove causation because it is true for 90% of cases. If researchers were to set-out to prove somethign that can only be shown correlationally you can sometimes get a good result, but most often you just have a correlation.

So just to clarify, it's your contention that we could never satisfactorily prove that gun violence had decreased in response to some change in regulation or legislation.

edit: i'm using the word "prove" here in a very flexible sense

I didn't read the thread (Don't have the time =/), but why do these conservative sites always propagate fear and then operate under the guise that they are "re-uniting America" and doing away with the "red-vs-blue mentality"? For comparison, FOX New's "Fair and Balanced" tagline.
It should be clear to anyone with an average intellect that these ventures do quite the opposite.

Also, these "socialist!" and "freedom hating!" comments are amusing.
We could discuss why those claims are unfounded, but I think the better question is:

When did capitalism, without restriction, become the best economic solution for a government's people?

(Side note: I'd prefer a nice discussion, not a "liberty-hating liberal!" comment, as there are more than two sides to a belief system, including mine. Thanks.)

EDIT: Apparently we've moved onto to gun control? Oh well, point stands.

Only criminals use guns to commit crimes.

 I am saying we will never, not thats we can't You culd try a series of long term studies where you periodically have or do not have gun control laws and see what the data starts to suggest. There are other ways to set-up a study that I can't think of that would prove it as well probably, but it will never be done. It doesn't really need to be done as we don't need hard proof to act. Strong correlations are good enough when combined with other forms of data.

I think the bolded comment might be a good place to start looking for answers to the other questions you were asking.

Fair enough:)

My other question (singular)? I'm not sure I follow.

It is a different outlook on their world, their life, and their country.  Most conservatives cringe when someone implies (intentionally or not) that the government has ownership of the people and not the other way around.  That isn't the whole picture but pretty much everything else follows logically from there if you give it some thought.

I see what you're getting at.
However, the way I worded it was intentional, as I was referring to economic systems, not our government (or any, for that matter), in general. If that is all my post communicated to you, then it failed miserably.

Past that, by stating that "most conservatives cringe when someone implies that the government has ownership of the people and not the other way around", you are effectively implying that liberals, and anyone in between, would not take offense to that same principle. A bigger government, economically, does not equate into less freedom. But that's another discussion entirely.