I don't hate it at all. In fact, I use it when it's called for. But the problem for many is that it is WAAAAAAAAAAAAAY over used. I heard a bass player in a COUNTRY band slapping about a dozen times the other night. Um..... there's no slap in country. (There's rap, and there probably WILL be slap at some point, but it's not here yet.) Plus, nobody wants to hear a Journey song, or Mustang Sally, or some old Motown with your musical jerking off plickity plackity fest during the whole song. Play what fits the song. If that's effects, slap, a pick, or a garden hose, fine. But if it's not, then just don't. If you simply can't resist slapping all freaking night, even when it's not called for, then you simply aren't mature enough to play. Go shoot things with BB guns.
However, if it's your band, your music, or music that calls for slap, then go for it.
And as far as that goes, learn EVERY technique you possibly can. Be able to play with a pick, with your fingers, slap, cop an URB with some foam under the bridge, pluck by the bridge, pluck up by the neck, tap, whatever. Learn it all and use it WHERE IT FITS.