Is it acceptable for YOU to do it?
No. It is inconsiderate of other patrons and may lead to the other patrons or yourself getting food at a lower than proper serving temperature.
Is it acceptable for me to take offense at some one else doing it?'
No. It is the restaurant's responsibility to manage these issues, make their customers happy, and get your food to you in an effected and sanitary way. Not yours.
Is it acceptable for me to take my business elsewhere if I do not like
the way the business handles this situation?
Yes. It is your money and you choose who to patronize and who to reward. The most effective way to promote a change in business practice is to take your business to companies that follow policies that you agree with. Be it with how they pay their employees, whom they support or do not support politically, etc.
Is it acceptable for me voice this publicly?
Some people will respect this, others will disagree with you and have issue with your complaints. Even if those complaints are more mainstream like the cleanliness of the kitchen. It is a safer route to voice your concern privately rather than publicly, a public display is more likely to affect the decisions of other people. This may come at a cost to your reputation of being a "Drama Queen" or the like.