As I said, I just don't accept that. You can't just say the words and have it be meaningful. Antimatter is more than "pretty dangerous." It's insanely dangerous. It literally cannot be touched without an instant kaboom.
That may be true, I'll even grant you that's likely the case (though are we sure there isn't something in the universe isn't actually more dangerous that antimatter--after all you yourself pointed out the spore drive is a danger to the entire multiverse). The point I was trying to make is maybe there are a number of factors why protomatter isn't used. It's dangerous, ok, maybe not as dangerous as antimatter, but it still can be incredible dangerous nonetheless. But there may very well be more than that. It was strongly implied in TSFS that Genesis failed because David used it, and he even said using protomatter was the only way to get past certain problems with Genesis. So maybe it's dangerous, unstable, probably expensive, hard to get, and finally maybe just not worth it, even to criminals.
My point was that there are a number of things said, and some implied in TSFS that Genesis was a dead end technology. And actually, in a way, unlike some of the here today, gone tomorrow technologies we've seen in Trek, they actually did provide a couple clues why Genesis was abandoned.
And they are doing that with the spore drive. But what confuses me is they created an incredible technology, provided a reason why it will probably be abandoned but yet the continue to use it. Now if I had to make a guess, eventually that's going to come to a head. I wouldn't be a bit surprised if there is some future episode where that comes to roost, where the Discovery is going to face the possibility of reality coming apart and them having to fix it and then eliminate the spore drive for all time. I actually hope something like that happens, because that would be a way to show the audience that it's dead and gone, and can never ever come back--that it can't be made safe ever.