Its just a cut price way of getting a band for the cost of a solo act
Undercutting other working musicians.Even if you do the backing tracks yourself it is NOT ethical

would this also apply to Keyboard players that are used to replace other instruments or midi guitars, harmonizers (bang goes the backing singers) - drum machines...... etc????

if there's the venue, audience and it brings pleasure - just pay your dues for the backing tracks... (keeps session musicians/singers in a job) and go for it!!!!

If people don't want it you won't get gigs!!