to me, a live PA must have a lot of spontaneity to be exciting. i want to see performers moving around, twisting knobs, throwing in loops on the fly, recombining elements into new tracks, etc.
some don't bother. even before laptop PAs became commonplace, some artists would simply create their live PAs before performing, and limit performance to some EQ tweaking. to me, this is worthless gobsh*te.
the problem with laptop PAs isn't any inherent quality of laptops or software vs. hardware, but rather that it makes it even easier to do this. or maybe the better way to say it is that more people act lazy behind a laptop.
that said, there's no reason they have to. this is a human failing, not a technological failing. a laptop-based PA can be every bit as exciting and spontaneous as a hardware PA, and given the unlimited potential of ableton, can be really, really exciting and spontaneous.