The terms "pro-life" and "pro-choice" are both terms intentionally adopted for polemic purposes, which is normal enough practice in many situations where there is disagreement and debate. For example in the names of political parties, such as Democratic and Republican.

The point being to adopt a label representing a positive and generally shared value, so putting the opponents on the wrong foot, by implying that they do not share that value. It's a debating trick.

"Pro-choice" does not in fact involve being anti-life as such, and "pro-life" does not involve being anti-choice as such. What such labels do in practice imply is a more restricted definition of, respectively, valid life and valid choice.