The title of the thread seems to be causing a bit of confusion. I believe it's not about slap in the Flea/Larry Graham sense, but more the tone achieved where (usually metal) players whack the strings to the extent that they 'slap' the frets and create a metallic clanky sound.
The title also causes annoyance for pedants who think it should read ' .....play it correctly'. :-)
Regarding the OP's question, I would refer to the quote in my signature. If people like the way it sounds, then it's 'right'. Just because that's not the way it was originally meant to be played, doesn't mean it can't be done. In fact, I'd go one further and suggest that this kind of open-mindedness and experimentation is crucial for moving music forwards. Trumpet mute, snare rimshots, thumb/slap/pop bass, all techniques which enrich the repertoire of the instrument.
Saying that, I'm not into that clangy sound at all, but 'right' is what the listener likes the sound of.