What I'm hinting at is, there's no such thing as lone ranger Christianity.
People either associate you with Christ, which colors their perception of Christianity; or they associate others with you, which colors their perception of those people. And the likelihood of someone seeing you walk out of a church, or associating with others they know attend a certain church, and thereby associating you with a particular church, is greater than we realize.
So, anyone who believes they affect only themselves, is extremely self-centered.