I think there's a couple of things at play here. As far as Kingdom Hearts III and the divide:
On one hand, the expectations for Kingdom Hearts III were so sky high, but more importantly, so varied that it was going to be nearly impossible to measure up. There were players who had played the entire series, players who'd willing ignored important entries, etc. In my opinion, there are legitimate criticisms of the game. Whether or not these overshadow the many positives is subjective to the individual player. Unfortunately, living in 2020 is a double-edged sword for art; there's never been more places to find people who share your enthusiasm, just as there's never been more criticism and hatred of the things you enjoy shoved in your face. My point is, whatever opinion you're looking to have backed up online, there's likely a place you can find it. For this reason, you should probably try not to be bothered so much by the seeming fanbase divide. I doubt it's as drastic as it seems on the internet where everything is either the greatest thing ever or the most disappointing. For what it's worth, KH2 split the fanbase just as much at the time of its release. It took time for people to level out and judge it with some semblance of nuance. I suspect the same will happen for KH3 and on some level it already has.
As for the overall attitude of gaming toward the Kingdom Hearts series, it's a similar thing. Who really cares what anyone else thinks of the things you like? It's very interesting how a majority of people that dislike or dismiss the series are very cynical, or uninterested in levity. Kingdom Hearts can be cheesy, and maybe stupid, or childish. But these are honestly some of the reasons I like it so much, it's a source of much needed basic good vs. evil story that makes me feel good. That doesn't mean I don't also like stories that are morally gray, complex, etc. I think the things Kingdom Hearts does well, it does very well and that's why it still has such a large fanbase today and keeps appealing to new people, nostalgia aside.
All in all I'd just say you do and like whatever you want to as long as it's not hurting anyone else. People who are going to bother you about it aren't worth remembering anyway.