The business transaction between me and a restaurant is for the food and service they provide. I pay the restaurant, the restaurant pays the labour.
Refusing to tip isn't refusing payment. If it were, I'd be illegal (i.e. theft). Labelling this as "sharing the labour cost" is precisely the problem at hand.
If I hand my pizza delivery driver a $5 bill, I intend it to be a bonus for the driver, not a subsidy for the business. I have zero incentive to pay the business any more than the prices they advertise.