Mexico is already corrupt without the drugs. Making them legal will give the cartels even more power because they will now be able to legally sell drugs in the US.
They already have (and know how to run) multi-million dollar operations, you don't think they won't think about legally partnering up with companies in the US?
"If certain drugs do have harmful effects then at least the effects will be mostly limited to the people who take them."
Many people want government-run health care in the US. Legalizing illegal drugs will add to the already large amount of addicts. Do we really want more addicts in our hospitals? I also don't feel like I should be forced to pay for your poor life choices. Regular Drug users should immediately get a huge increase in healthcare costs.
We still have tons of people suing the cigarette companies because they cause cancer. I can only imagine how many lawsuits will be in our court systems if there is a company selling heroin.