Are you below 4.0 level? Or new to tennis?
Once you start to play against some higher level players, up to say....5.5, you will find it don't matter! A slice with little pace can work as an effective passing shot, if it's hit low over the net, and you set up the volleyer with previous shots.
Yes, you DO need a fair amount of topspin to pass MichaelLlodra when he's camped at net.
Chances are, you aren't playing Llodra. You are playing someone close to your level, so a slow moving, no spin, even underspin ball, is good enough for a winner.