Alright so first off, driving high compares nothing to driving drunk or anything of that sort. I have driven baked off my ass so many times and i've found it 10x easier than driving while fatigued.

Yes, a large portion of people who want it legalized already smoke it, but there are many who would like to try marijuana, that don't because it's illegal(in most states).

but I don't get when you say this

"You smoke it, and presumably get away with it anyway, and have shown that you are willing to disregard the law (unless you live somewhere this is already legal). If you're going to smoke it anyway, what difference does a law make? Smoke it, fine, but don't push to make it legal and encourage others to take up the habit, as it inevitably would. At least the law will stop more honest people who would be otherwise compelled to smoke weed."

Many people realize that there is pretty much no negative effect to the intake marijuana as long as you're safe with it and keep your priorities straight. No one is pushing to make weed legal in order to encourage others to take it up? Some would just like to smoke without the grim thought of "oh shit this is illegal, hope i don't get caught." running through their head. Most people just want to partake in a harmless activity, in the safety of their own home without having to go to some sketchy street dealer and wait 45mins for them to show up and not even weigh it out properly.