It's just the slippery-slope fallacy: if X then obviously Y will follow, and there will be no further decisions, debate or time before it does.
One of my many peeves has been the way that people misuse the term “slippery slope” as evidence for their stance.
“If X, then surely Y will follow! It’s a slippery slope! We can’t allow X!”
They call out the name of the fallacy they are committing BY NAME and think that it somehow supports their conclusion?
I rhetorically agree it's not a good argument, but its use as a cautionary metaphor predates its formalization as a logical fallacy. It's summoning is not proof in and of itself (i.e. the 1st amendment). It suggests a concern rather than demonstrates. It's lazy, and a good habit to rid oneself of. But its presence does not invalidate the argument.
Yes, it does. The problem with the slippery slope is that the slope itself is not argued for. You haven’t shown the direct, inescapable causal connection between the current action and the perceived very negative future outcome. You’ve just stated/assumed it. That’s what the fallacy is.
The doomer utilitarian arguments often seem to involve some sort of infinity or really large numbers (much like EAs) which result in various kinds of philosophical mugging.
In particular, the doomer plans invariably result in some need for draconian centralised control. Some kind of body or system that can tell everyone what to do with (of course) doomers in charge.