The reason we Americans are so strongly tied to our Constitution is multifaceted, but one of the key tenets is that it is a so called "living document" and allows itself to be modified via an amendment. The criticism that it should not be made illegal is a criticism that we are directly in violation of a document with extremely clear language. Instead of doing so, we should do the "correct" thing and pass an amendment to correct the original language with our current up-to-date understanding.

It is my personal opinion that the reason we don't is because enough people disagree with modifying it, and so it has to be curtailed slowly (rightly or wrongly.)