Earlier quoted context omitted.
Why would you ignore the tip? Points one and three are valid, and you should always hop in before you direct, but ignoring the tip on what is essentially a luxury good (metro is $2.75 a ride and you can transfer as many times as you need to get where you need to go) is quite rude when it's expected and part of the culture. If you can't afford to tip your taxi driver, take the train. Sorry.
That is no justification for the driver to be rude or snarky.
In certain Asian households it is expected that you take your shoes off, if you know this, and still stomp around the household in your shoes, would you say there was no justification for the owner of the household to be rude or snarky?
You might be able to argue that the enlightened person might say "I don't know what has happened to this person today, or why they're doing this, and I will try to find out their story before assuming they're just being an uncultured ass", but there is certainly justification, especially when it comes to the fact that these people are earning their livelihoods in this way and the tips are an essential part of that.