Regulation shouldn't cause harm for causing harm's sake. We already know prohibition doesn't work, so why did they drag their feet on repealing regulation that is both harmful and ineffective, is my concern.
Also to answer your question about weed stocks: I used to own cannabis stocks but dumped them about a year ago. Big mistake! They've doubled in price over the last week presumably from this news.
My actual issue with this is:
a) it should have been done sooner. Waiting until $election_year to do something popular has severely damaged the growth of cannabis industry
and b) it's another executive branch rule by decree that could be reversed as soon as 6 months from now after election day.