Any compassion of one issue in one society against the same issue in another society is bound to be a 1-variable fallacy.  Societies are shaped by many, many factors.  The factors which can be quantified are usually many in number.  Making such heterogeneous comparisons and claiming that only 1 variable is responsible for something is akin to arguing that the main difference in taste of fried eggs and sushi is that sushi has more salt.

If you want to evaluate how good a sushi is, you compare it to another sushi roll of the same kind.  If you want to evaluate how well a policy functions, you evaluate it against a different implementation of the same policy in the same society.  So rather than comparing more guns in the US vs less guns in Europe, you can compare more guns in Australia vs less guns in Australia.

You can't do that with the UK (pre-gun-ban vs post-gun-ban), either.  UK has (or at least has the reputation of having) curtailed civil liberties since making guns illegal (so it's  not a comparison of 2 like societies).