If he never touched coke and only smoked weed, but couldn't keep it together and became a complete wreck everyone would have the same criticisms. Coke just has a much higher capacity to turn a relatively upstanding citizen into a balldo-wearing, wife-swapping, child neglecting reprobate.
Weed can turn you into a lazy amnesiac, for sure. But, it is more akin to alcohol in the respect that, imo, it can be used relatively responsibly. Coke is a different ballgame. Coke allows you to drink way past your normal limits, and is probably why we've seen him repeat AnimeSucksCopeAndSneed chats 9 times; he's so fucked, but still running on fumes because the coke allows him to stay awake. Coke and alcohol combined creates Cocaethylene, which is far more toxic than either separately, and has led to his rapid degeneration.
That is to say, not all drugs are equal.