Our advice is to be as polite and courteous as possible. If they're upset about being contacted, graciously apologize and wish them a nice day. If they reply angrily and ask to be opted out, again apologize, and mark them as DND.
Often times people are angry because they assume they're being texted by a robot, so if you reply to them apologizing, people tend to be much less upset. We've seen many cases where the recipient replied angrily about being contacted, but after receiving an apology text, they replied again with a much softer tone expressing appreciation that they received a response at all.
Responses are important whether the recipient replies positively or negatively. Remember that the best part of peer-to-peer is the fact that you get to have real conversations with people, and everyone wants to be treated kindly.