Sanctions slow down advancement, but they don't stop it. Someone, somewhere is going to say "fuck it" and build it regardless. What they can do is ensure that

Sanctions slow down advancement, but they don't stop it. Someone, somewhere is going to say "fuck it" and build it regardless. What they can do is ensure that the sanctioned entities are always at least a generation behind. That's not especially helpful in the context of "anti-doomers will be wrong exactly once" unfortunately.