We are constantly telling that simply because there are no other routes available as of right now except the harem one ( so if you don't take all the girls you will be brushed off on how the story develop, since all the characters are actively involved), not because we are trying to guilty trip everyone to get only that, is different.
Imho Killer did the right choice focusing on the harem, trying to branch from the start all the girls route considering the amount of main LI's and side ones would have been a nightmare, and the game would have been in his early stages instead of being nearly finished.
Too many games got stalled for that ( just look at what's happening with WVM just to give an example).
Once the alternative routes will be implemented ( we don't know when), the game will have more freedom of choice I think.
Imho I will still stick to the harem anyway, but that's my opinion.