I guess we'll have to agree to disagree. Any server who asked me if I was done with my plate (or just whisked it away without asking) while I was still actively eating? Isn't getting (much of) a tip. If the server immediately realized they'd had a d'oh moment and apologized, I'd still tip but probably on the low end of normal.
Actually you said you would still doc them. When you make a minor error at work does your paycheck get reduced? Expecting perfection from 18-23 year olds is ridiculous. Keeping track of every perceived error and systematically reducing a tip is rude and unfair.
I would lower the tip. The tip comes from the waiter helping me to have a really nice meal. If my water glass is kept full. If I am offered refills on drinks I pay for, if I don't need to look for the waiter to get a spare napkin, if I barely notice that the waiter is there because they are around when I need them and not when I don't, then they get a higher tip.
I wouldn't stiff the server over a single mistake, but it factors in. That is the point of a tip. There is a base level that I tip as long as the server does not refuse to bring me my order or hurl abuse. Then there is a range above that based on the pleasantness of my experience.
No the point of a tip is so someone can pay their bills and take care of their family. Not for you to play god or boss in your 45 minutes with them. When you (general) receive a service you pay for the service. The only difference in tipping is that the server doesn't have any recourse if you don't leave one. They just have to hope that the next person can make up the tip out they have to pay for your meal.
If the service is so appalling that you think a drastically reduce or no tip is deserved then you need to speak up in a way that something can be done or keep the experience in mind next time you're deciding where to go.
The point of a tip is to reward good service. If the person believes they have not gotten good service, they are well within their rights to diminish a tip. It is most certainly not to help someone "pay their bills and take care of their family" - if they were given money without earning it, we would call that charity.
You say when you receive a service, you pay for the service. Well, what this poster thinks is that she received her food, and she paid for her food. But the service component (the well-delivered meal with attentive service that did not rush her out of her seat), was not delivered. So she reduced her payment for that service accordingly.