Usually if you want to have some kind of civil social dialogue with people who have a different POV than you, the best start is to call them by the name they prefer. It shows charity and respect for them as human beings. We are always called to ascribe the best of motives to people, even those we think are very wrong indeed.
As well, many people who in some way support the legality of abortion are not, strictly speaking, pro-abortion. Most probably aren’t in the sense that they think it is a good idea for people to go out and get abortions. So they resent being labeled in a way that seems inaccurate to them. As if they labeled pro-life people “anti-choice” (which some do, and it ticks off pro-life people.) By saying pro-choice, it shows that we understand how they concieve their position.
And calling an opposing POV by a name that brings up the worst possible connotations is a way of emotionally twisting words to make people agree with you. If there is a good argument about abortion, it should not require that. If you are trying to stop the discussion before it starts, then it is a way to do it.