Since the first century, the Church has addressed the moral evil of abortion and the killing of a defenseless baby in the womb.
People who are casual about the sin of abortion and who choose to view it as a political issue rather than the serious moral issue that it is are guilty of violating the Fifth Commandment.
You cannot be "pro-choice" (pro-abortion) and remain a Catholic in good standing. That's why the Church asks those who maintain this position not to receive holy Communion. We are not being mean or judgmental, we are simply acknowledging the fact that such a stance is objectively and seriously sinful and is radically inconsistent with the Christian way of life.