Admittedly Portugal isnt a 100% example, but its the best we have and the evidence we do have, shows that it is not a terrible idea. Sure, I don't think being able to go to the gas station to buy PCP is a good idea, nobody should do PCP, but picking and choosing what people can and can't do is a slippery slope.
As for methheads stealing your TV, why are they stealing your TV? because they need more meth, and meth costs a lot of money. To get the money that they need to spend, due to it being illegal, they steal your TV. They don't take a hit of meth and go "omg... you know what sounds like fun??? stealing TVs!!!!"
Also, most of those issues are about misuse. People will misue things if thats what they wanna do, with or without your permission. All being illegal does is make it ney impossible to get any real info. So when the kid gets exposed to meth, he has no idea that it isnt just like weed, and tries it anyway without knowing the real risks. He knows the gov's full of shit, but thats about it. Sure they give some real info, but its watered down by so many lies it doesnt help. My 11 year old brother the other day heard a joke about crack and he said he knew about it and I chewed him out. I asked him what he thought it was and his answer was "a type of weed". I always play the "drugs are terrible, never do them" with him, he has no idea everyone around him smokes. That is great for this "innocence" but the gov has been beating this innocence out of us for a long time. The only thing to come of it is misinformation. Sure, maybe a few more people would do that "one try" but so many more of those "one try" people would stay at "one try" simply because they would know the real deal and not just guess at it.
I grew up smoking and looking back, I was so dumb it hurts. Do you have any idea how many people have no idea that you smoke the flowered buds? I have heard tons of stories of little punks growing a plant like 1 ft tall, then smoking the entire thing. It isnt there fault, I see posters and "information" everywhere stating that you smoke the dried leafs. Disinformation is more dangerous than any drug (except maybe meth and PCP, admittedly I wanna pick and choose a few drugs to stay off limits, but I would feel like a hypocrit doing that, which is why I support full legalization).
So, If they legalized just weed, I wouldn't really fight for everything else, not worth my time, or energy. I agree some drugs are just plain bad, its more of a moral thing.