I would feel different if the culprits were Jones or Smith, for it would be the responsibility of the US to take care of their citizens and suffer the expense of prosecuting them. However, when they are Mexican, why should the US have to spend to take care of Mexico's problem? This is not being a good neighbor.
I don't mind helping their law enforcement agencies, provided we can do so in a way that doesn't tip off the drug smugglers. But it is bizarre that they expect such actions to be matched by huge U.S. concessions on immigration policy.