Good slap is a valid and effective technique. Bad slap is "circus bass", just pointless tricks and noises. So good slap works in the context of the song. Bad slap is usually someone showing how clever they are in a solo.
My first attempt at slap came when I first heard Thank You by Sly and the Family Stone. I have to admit, my efforts since have been pretty half hearted. I haven't had much incentive, I've never been asked to slap in any band and none of the bass players in the other bands I see use slap. One singer even thanked me for not slapping! Slap (tapping, chords and harmonics) are totally missing in the musical world I inhabit.
Two months ago I had such high hope for my technical improvement during lock down, and all I've done is play stuff I know. Maybe I should get the Jazz out and start learning "good" slap.