You can't really "back up" an opinion. If someone's opinion is that BaD is the greatest game that ever was then no amount of contrary discussion is going to convince them otherwise. People enjoy different things. Some people worship the ground DPC walks on, others not so much. People like what they like. Someone liking or not liking BaD doesn't invalidate anyone else's personal opinion.
I disagree, I think you should be able to back up your opinions, if not why are they your opinions? I guess there is a difference between personal opinion and evidence Based opinion. While I think you’re right that fanboyish ‘greatest game ever’ types aren’t likely to change their minds based on someone else’s opinion, if you can back up what your saying rational people (which is the majority here) will listen.
I’ll give you an example, I think DPC has some of the best artwork out there, but he does have a bad habit of overmorphing his models face’s. Examples ranging from Josy, who can look odd from certain angles, to Jill who looks terrible with certain facial poses to Cathy who looks like an alien. I can show artwork that backs this up, however if on a personal level you find aliens hot, that’s not something you can be convinced to change your mind on.
Writing is similar, I think for the western porn visual novel genre DPC is up there with the best. I think it is undeniable that the complexity of the the choice based consequence system is beyond anything anyone else has produced. The quality of the prose is good, but again if someone wants to challenge that they can. However if they do they need to give examples of all the better games. People can’t do this in significant enough numbers to relegate DPC to average let alone bad. However when it comes to genre, that’s just a matter of personal preference, don’t like college comedy/ melodrama? Well then of course you’re going to hold BADIK in lower regard than a genre you do like.
As for mechanics, again there are two ways to look at this. How are they implemented and do you enjoy them. For example I think they are all well implemented. Are they all fun? No. For example I think the classes are a mixed bag, English is annoying since some of the words aren’t words, maths is fun if you like problem solving, and Women’s studies sucks because I have a terrible short term memory. I think tennis is fun and take what in other games would be a couple of images one after the other and makes it something unique. Then you have the house repair mini game. I love this, I love micro management strategy stuff, but if you hate that, that‘s an opinion unlikely change through debate.
My point really is if you want to critique something, you should be able to justify that criticism. In a lot of ways this should actually be easy for people since it’s easier to criticise than it is to praise.