I have changed my mind a bit on this topic. I tried to explain my thoughts about this on reddit but got downvoted into oblivion - before eventually getting upvoted once people started to understand the point I was making:
Legalization makes sense. Legalization of ALL substances, to me, makes sense. I don't see any reason why any substance should be illegal. Laws currently don't stop people from attaining any substance that I'm aware of, regardless of age. Hell, I first tried pot and alcohol at 13 and I'm sure many other people have too.
Regulation, on the other hand, does NOT make sense to me. Taxation is theft and therefore, taxation of marijuana is ALSO theft. Also, it means that the government is going to have a lot of control over the substance you are ingesting, which is arguably just as dangerous as not knowing the source you are getting it from in the first place.
Regulation/Taxation in general are dangerous because they allow the government to create arbitrary laws which expand control. That's how things like war and poverty get created.
So, I am ALL for legalization of marijuana and ALL other substances, but I am 100% AGAINST regulation. I think that the government at this point is sort of tricking marijuana users into thinking they are doing a good thing for them, yet all they are really doing is expanding control.