I think I recall this also being referred to as “the slippery slope”. It’s the fallacy that one thing will lead to another as a negative consequence. So to put it into context, an Adult Virgin might be tired of the VCard approaching the thirtieth birthday and so considers going to an escort. Now this might or might not be a good idea, but to say, “No, it’s a bad idea because if you like it then you’ll need to keep doing it, then you’ll be a sex addict, then you’ll be hanging around a load of seedy brothels and will get drawn into drugs etc ” Obviously, you cannot say that will happen, so it’s an illogical fallacy.
Or, you could think, “What if I ask that girl out.. and she says yes, and we really get on, and we get married, and have kids, but it doesn’t work out and we get divorced and I end up with alimony obligations”. Well, that might happen… or this slippery slope might not.
This distortion is linked to the cognitive distortion of fortune teller error.