When it crosses state lines and that's about it. Why the Congress has to "allow" States to exercise their 10th Amendment rights is beyond me. This is where Ron Paul is a hypocrite because he is admitting that Congress has such a right rather than siding with the 10th Amendment.
So make the case how the fedgov can prohibit someone from growing a few plants in their own house for their own use.
That's not correct. See Wickard v Fillbvurn and Raich v Gonzalez
Fed Gov also become involved when it is smuggled across US borders. Considering our inability to stop it when it is illegal in the US, I dont see how we are going to stop it if it is legalized — even on a state by state basis.
Just like with legallizing illegal immigrants vs stopping illegal immigration, we need to secure our borders against illegal trafficking before we legalize illegal drugs.
What about the rest of the Congress that keeps this unconstitutional law on the books and funds it every year with billion$? They are not only hypocrites, they are violaters of the original Constitution.
Focus your scorn on fedgov drug warriors where it belongs.