Complaining about tax on these separate transactions is like complaining that you had to pay income tax on $5 that you earned at work, then when you go buy your morning coffee you have to pay sales tax on that, and the coffee company has to pay taxes on the profits, and the barista who served you has to pay taxes on his income, and then so does the coffee bean supplier etc. etc. etc. etc. That's not what people are complaining about when they complain about double taxation.
Once you understand this you will complain about double taxation in a whole new light.
Lets take your Barista example, keeping it super simplified:
Zero Cost of Product (I know its impossible, but it keeps the numbers clear for the example)
Sale Price $5
Salary to Barista $5
Sales tax 0%
I buy 1000 coffees in 1 year. Cost to me= $5000
The Barista earns $5000 in salary from the coffee company from the cost of the coffee
The coffee company earns income of $5000
When the IRS comes a knocking, the coffee company says 'I don't have to pay you 1.5K because I paid that to my Barista as salary, it is a cost of the transaction'.
The Barista still has to pay 1.5K, but that is it - they aren't asking the coffee company and the Barista for the money.
However when you Tip - you cannot deduct the tip, and they are asking the coffee company and the barista for the money...
Get it?
I'm not even talking about sales taxes and all that - I am saying that from me to pass money from coffee company to barista - just pass it, not profit from the transaction at all, I have to pay 1.5K?
That is unfair.
As you can see I use the term Unfair, because I am fully aware that is what the IRS wants so don't worry about my comprehension of it, I know how they are scamming us and just think it is unfair.
Think about it some more.