Are you pro or con being courteous polite and respectful? Why?

Pro courteous, polite and respectful.

Respect is the key.
All sentient beings deserve it because all are capable of suffering - unconditional respect from the moment of birth.
And it's hardest to apply when angry.
Being disrespectful only ever backfires. It raises the ire of the other, leading to escalating negative results.

Courtesy is the behaviour that naturally results from respect.

Politeness is just a cultural protocol or expectation - a way of soothing out the potential bumps in social relationships.
It changes across cultures and socio-economic groups, which means one has to be sensitive about who one is talking to and their background.
In most English-speaking cultures it amounts to:
please, may I? excuse me, thank you, I appreciate, how can I help? how can I make amends? and, I regret because ...