Because our laws are created by politicians.
My personal take on this is that while Law (legal) issues and Civil Rights issues have a political import, they are not politics directly. To me, politics is about the people in politics, their views, their proposals, party platforms, etc., and the interactions they engage in. In other words, what they are doing today, and proposing to do in the future, and especially the why.
We have agreed that a certain amount of political discussion cannot be avoided, and I think proposed legislation falls squarely into that category. What we need to avoid is personal attacks and value judgements on the reasoning of the legislators. As noted that are lots of other places for that.
Policy is another issue, and one that has tremendous legal repercussions. Again, I believe we can discuss various policies without resorting to giving our personal opinions of the individuals who create and implement that policy. For example, I have a very specific personal opinion of those individuals who created BATF policy that lets them define a single firearms part measuring less than 2"x2" as a machine gun, all by itself, but you will not read that opinion here.
Remember, pointing out the mud on someone else's fins does not improve your own swimming.