The problem is all of this activity is already illegal. Banning a bunch of semi-auto rifles in the US will do nothing to slow the flow of arms into the hands of the cartels.
This has nothing to do with the gunwoobie. I did not say anything about corrupt dealers as there are certainly corrupt dealers selling to straw men but that is already illegal. You can't make it anymore illegal.
The problem I and many others have is the AG insinuating that an AWB will stop the flow of weapons into Mexico. Since the activity they are trying to stop is already illegal is there really a need for more laws. You said yourself that the laws for combating this are already on the books.
As you mentioned Mexico is corrupt and needs to fix its own house before they demand others do it for them. We should certainly demand an end to the corruption. Corrupt government officials looking the other way can certainly make it very easy to smuggle arms.