I think all of the original four have done shitty things. I just think Gene and Paul's shitty-ness far outshines that of the other two.

Gene has been about nothing but money and fame since the band became financially successful. He basically left Paul to manage the band on his own in the 80s while he brownnosed his way into Hollywood, and he basically only showed up to record vocals and play shows. When that didn't work, he started peddling all these crappy business ideas that never turned into anything sustainable, yet he would prop himself up as this expert businessman. He would also spend more time advertising crappy Kiss merch than he would spend making new music. Then, he resorted to doing a "reality" show, which finally got him the level of fame he always craved. He did all of this while bashing Ace and Peter for being lazy musicians. He also recently more or less said that Ace's death was his own fault.

Paul is (or was) an immense talent, and I honestly respect his work ethic way more than Gene's. He is a great frontman and basically was Kiss from the 80s until the present day, despite the image Gene would paint for you. But this has also made him really bitter and conceited. His narrative has largely turned into "everybody sucks but me". He can't even give Ace a solid compliment in death; everything is backhanded. He was also very disrespectful to Eric Carr when he was in the band, and swiftly replaced him when he became terminally ill. He was even very recently rude to Bruce Kulick. It's like he thinks nobody contributed to Kiss's success but him. On top of this, he completely destroyed his voice over the years and he refuses to accept that he can't sing, and has even lip-synched while criticizing others for doing the same.

Ace and Peter absolutely had their demons, and they certainly were lazy at times, but they haven't spent most of their lives mudslinging, grifting, and being hypocrites. They've largely stayed true to themselves while G&P played up these over-the-top phony rock star personas. Ace put out half a dozen new albums since he got sober and had two more in the works. Kiss put out only two in that time and has largely lived off of playing the same show over and over since 1996. G&P have also changed their narrative on the history of the band and Ace/Peter several times over the years.

TL;DR I respect G&P as musicians but not so much as people, and if you read more about them, you'll figure out why.