I'd be lying if I didn't say Flea wasn't one of the reasons I picked up a bass in the early 90s. The Blood Sugar Sex Magik album was (and to a degree still is) my bass bible, albeit notable for its lack of slap bass compared to their previous output. Whilst RHCP have completely jumped the shark these days, I'm still a huge fan of their early output and the bass playing on it. Whilst a lot of what he plays isn't that complicated, the speed and energy he plays with made it unlike anything anyone else was doing at the time. Obviously having Chad Smith as your drummer helps a great deal too.
I have nothing against slap when it's done well. The problem is that it rarely is! Like a lot of things, it's an easy concept that's hard to master.