Obviously people can say whatever they want, but I personally don’t see any value in dragging something down when instead I could be lifting the thing I do like up.

I can understand that. It's no fun to rain on someone else's parade. But I don't think there is no value, for example, in you expressing why you dislike Picard Season 3. You'd be dragging it down, but I don't think that's so wrong to do. It's okay to dislike things, and it's okay to say you dislike things. I think you agree with that.

Like, imagine going in to the job at the end of the week and saying, “Hell yeah, I love Fridays!” and some sad sack co-worker is all, “Yeah, but don’t you just hate Mondays?” Buddy, why? What would be the point in being so negative, when instead you could be positive?

The co-worker sounds like no fun to be around. But what if the conversation was this:

“Hell yeah, I love Fridays!”

“I'm with you on that, this week's been rough.”

The co-worker isn't trying to bring you down by reminding you of next Monday, they are trying to relate to you over your shared experience of the last week. You may dislike it, but I don't think it's the same as them going "but don't you just hate Mondays?", and I think that's more like what is happening when people talk about their dislike of some show.

Now, imagine if every time someone made a post praising, some other series or new episode, I jumped in with, “Yeah, at least this one was better than season three of PIC.” What am I actually contributing to the conversation?

Not much at all. But if you did it once, it wouldn't be fair for me to treat it the same as you doing it every time you reply to someone. I'm not suggesting you bring up your dislike of Picard in every conversation – I agree that would be annoying – but, if you have a point to make, I think it would be fine for you to on occasion bring up Picard's flaws to highlight the strengths of another show. I think it can even make your point stronger; instead of contextless praise, you can point to something specific to show how one thing is an improvement over another.

People do this with Voyager and Battlestar Galactica, where they praise BSG for commiting to the premise in a way Voyager didn't. I haven't seen Voyager and I haven't finished BSG, so I can't comment on whether I agree with that, but if someone agrees with that criticism and prefers BSG to VOY for that reason, I think they should feel free to criticize Voyager, to praise BSG, or to do both at the same time. Perhaps the contrast can be illuminating.

Furthermore, I don’t consider, “This doesn’t feel like [X],” to actually be criticism.

Sure, I agree with that. But if the criticism is bad, it's bad regardless of whether or not something else is being praised at the same time. It seems that you think it's worse to praise and to whine than to just whine.