When confronting foreigners who wonder why we let stupid laws (rest assured, there are many and we know) take effect I can only say this....
We, Americans just don't want to be concerned directly with monitoring every law that goes through congress, even major ones. Obviously I can't speak for everyone. And to avoid being blue-crossed i'm not going to pretend like I know the logic behind it, but I think most law abiding middle class and working class citizens in the U.S. would agree.
In my opinion, it's just that we trust representative democracy a lot. Enough that when we directly elect local representatives, we hope that they have enough common sense and understanding of the general population to try to prevent stupid-ass laws.
In short, we prefer to handle our personal problems and trust the elected officials to be sensible about lawmaking. The law system in the U.S. is pretty damn complex. And after all its their job. We don't want to have monitor everything and do their job for them.
Unfortunately it seems to be failing us with more frequency recently, it seems.
TL&DR: Demcracy is awesome! Or, "Don't you worry about blank! Let me worry about blank!"
Edit: Sorry about all the big words.
Also, to answer your question why we don't react: Read above. If laws go through the process we usually just trust they're for our benefit.