Am I Sinning by Not Ministering at an Abortion Clinic?

Abortion is one of the flagrant atrocities going on in America, and Christians should be involved in taking a stand against it. But how exactly are Christians to be involved in combating against it? Must we all stand in front of an abortion clinic and protest? Are there other ways to be involved? What should we think of Christians who are accusing other Christians and other churches of being in sin for not going to an abortion clinic to protest against the murders being committed?