Personally I don't so much mind pregnancy being a bad-end-only thing, it's just annoying when it's only a possible result for one specific scenario, and then it gets added into the tags. If the MC getting pregnant leads to a bad end, that's fine... It is reasonable, actually - in erogames with a more fully realized pregnancy system for the main character, they end up having to either make it mandatory for the heroine to get an abortion, or include some contrived elements allowing for the game to continue (usually some kind of magic that hyper-accelerates the process). In fact, the only time I've seen a game that both allowed the heroine to get pregnant and didn't include magic was 'Civilian Justice League 2' where the heroine takes 9 months off when she has a baby... and considering that that's in the context of a large-scale war going on with gundam-esque mechs, that raises its own questions, especially if it happens more than once or twice.
So yeah, pregnancy bad endings aren't inherently bad, but they tend to be very same-y (it's always "life of sex slavery forever with mind-breaking") and when it's only a possiblility in one or even two scenes, it's annoying to have it included as one of the tags.