An acquaintance of mine, (I wouldn't call him a friend, and you will soon read why) had this same discussion. The legalization of MJ.

I was for it, he was stone cold against it. He is a small time grower/dealer. I was stunned to hear him say that, so I ask why. He proceeds to tell me that it would put him out of business. He tells me that he sells about a tad over a pound a month. He charges normal prices, I've purchased off him on a few occassions when my supplies were running out, usual prices, 30/60. Thats close to 4k a month which is almost 50k a year, (whoah never did the math before, thats alot of cash)
He says that legalization would make him homeless. That "selling pot since he was 16" is the only thing he knows. I'm sure there are alot of people that are here of this mindset considering most people here, but talking about selling their wares is taboo. I believe that if it's legal, prices would drop considering any "joe shmoe" and "grandma bee" would be able to grow it.