Tips to wait staff are voluntary but have significant social pressure behind them. Tip jars at counters have no social pressure behind them. That's not reductive, that's just the practical reality of tipping culture in America. If you refuse to tip a waitress a very significant portion of the American population will consider you tantamount to a thief, a morally bankrupt person. Refusing to put your change in the tip jar doesn't even cause people to bat an eye. The social dynamics between these two scenarios are worlds apart. Ignoring these disparate social dynamics is reductive.

If you're going to be outraged that Starbucks offers you the opportunity to tip people at the counter, perhaps I should feign outrage that you spend your money on starbucks instead of making your own coffee and giving the difference to the homeless. Starbucks has a significant profit margin after all; that is money you could be donating!