[john70t]

I suspect the $15 is not the primary reason.
But only the tip of the iceberg.

In any properly staffed and busy restaurant, raking in hundreds of dollars per hour, that hourly-wage difference equates to about a minute or two actual loss.
Actually the higher wages might even be a gain when using some economic models.

Happy employees pull in many more happy customers.
Much like dance clubs that pay wild girls or casinos that comp or start-ups faking web attention. (i.e. McDs "I's be lovin' it.")

I think the protest is human rather that factual:
Americans are prone to overdo everything and blow anything out of proportion.
Every single thing has to be documented using triple carbon copy paper.
A bad look is a wrong look. Talk to my lawyer.
"Get the hell out you're fired" has a deeper subjective and reflexive and sex/race/other biased explanation rather than you taking a crap in the lobby.

Corporations feel threatened?
A human employee apparently is more a liability and expense than a machine?
Or will most humans willingly choose Solylent Green even after it's explained to them.