I've also been criticised for sideslipping. Personal theory is that it's so uncommon it scares people who might not be familiar and current. People fear what is out of the ordinary. Try landing a pitts without sideslipping
Now, caveat emptor: this is most likely entirely type, and possibly aeroplane specific, but I went out and deliberately stalled a decathlon in a full blooded, rudder on the stop sideslip. Guess what it did?
Stalled. That's it. No wing drop, cleanly and straight ahead. No drama. Who'd have thought it?
No guarantees that all a/c will behave in such a benign manner (and I am in very regular spin practice), but my take is that a rate of yaw is required for a spin. In a steady sideslip in a straight line both wingtips are travelling at exactly the same speed.