Rand Paul calls for allowing states to make their own drug laws. He doesn't want federal "LEGALIZATION"\
The liberty position is to not fight for LEGALIZATION on the federal level because that implies a law being passed to make it legal, which the constitution does not grant congress to do. He wants to decriminalize and ultimately eliminate all laws regarding drugs.
Think of this issue as foreign aid. Rand wants all foreign aid to be gone. Israel is like Meth. If Rand advocates making meth not illegal federally and campaigns on it, it would be more politically suicidal than stumping on cutting aid to Israel. However, Egypt is like marijuana. There is more pressure to end foreign aid to egypt. There is more pressure to eliminate marijuana laws.
When evaluating positions, we need to find guys who want to move the government in our direction (that is less government). If the shift is minute v. Drastic.... who cares as long as the government gets smaller. If the political will is only their for Marijuana, we should fight for marijuana and get it done. Who cares if we go one drug at a time. Real change takes a long time.
Rand Paul is taking the pragmatic position. He knows advocating for eliminating all drug laws will make him lose so he advocates small changes and keeps pushing to slowly eliminate drug laws. He's a slow libertarian. He wants to slowly move the government our way. He is on our side.