The courts exist for this purpose, but they aren't supposed to have to make a ruling for EVERY law. It would be very wasteful if lawmakers did not think at ALL about whether their laws would pass court scrutiny. Some laws are so obviously unconstitutional that they should not even be attempted; that will just waste taxpayer dollars. Of course, lots of things are in a grey area... that is where it makes sense to try to pass a law and see if the courts agree.

But for most of the time, lawmakers should try to only pass laws that are clearly legal.