Define "bad vocalist."
Explain how this question is different from "do you like Kiedis's vocals?" or "do you like RHCP?"
Objectively, Kiedis is (I believe) the only lead singer of a band that has had a 35+ year career, has sold upwards of 80 million records worldwide and has won over a dozen Grammys, AMAs, VMAs, etc. Thus, it cannot be argued that he is anything other than a massively successful vocalist.
Is he an objectively good singer? I'm not really sure what that might mean, but I don't know the answer.
Do I like RHCP? Maybe one or two songs are ok, but as a general matter, I don't. Is my general dislike for RHCP primarily attributable to Kiedis's vocals? Probably not -- i.e., it's not as though I'd like the band with a different singer. I just don't care for the band's style. I can't stand his vocal performance on "Give It Away," but that performance is appropriate for the song. Moreover, I would say that all of his vocal performances have been appropriate for the songs.