Today, Vermont became the fourth state to legalize Gay Marriage. The list now includes Vermont, Connecticut. Massachusetts and Iowa -- and the momentum is growing. Washington, DC also has just voted to recognize Gay Marriages, though the approval of Congress is still required.
Marijuana will probably be legalized soon, too. These are all political decisions. Lines must me drawn somewhere -- based upon states' rights and the will of the people in each state.
When the voting age was lowered to 18 from 21, one might have argued: "Why not lower the voting age to 16? After all, 16-year olds are allowed to drive, so why shouldn't they be allowed to vote?"
It's a political decision. The lawmakers and the people decided that 18-year olds should have the right to vote, but not 16-year olds. Similar distinctions are now being made in these other social areas, as well.
Gay Marriages are rapidly being legalized -- but not incestuous or polygamous marriages.
Likewise, marijuana will be legalized in many states before much longer -- but not other, more destructive drugs. Medical marijuana is already legal in California, since the drug apparently has some beneficial effects and its harmful effects are no worse than liquor.