"It should be made a law that Congress (or for that
matter, any law-passing authority, this problem exists
not just in the US), should before passing any law
evaluate its impact and interference with already
existing law."
Ironically, that law would have so many impacts on so many other laws, it would be impossible to evaluate them all.
It's already the law...Congress already has several agencies that deal with these sorts of analyses. The most famous are the Congressional Budget Office and the Congressional Research Service. They deal with this silliness all the time, so they're actually quite good at it.
It's the halting problem for lawyers. :)