You also send a message to those you are separating from, that they are doctrinally or ethically in great danger. Withdrawing our fellowship is a strong method of showing our disapproval. Another reason of at least equal importance, is one's own spiritual life. Listen to a lie long enough and you might begin to believe it. Your spouse and children may not be as discerning, their spiritual lives are also at stake.
Spiritual matters are by far too important to compromise.
Remember that if you don't stand for something, you're likely to fall for anything. Disassociation is an individual's response to false doctrine or unethical conduct by another person, a ministry, a church, or even a denomination. Excommunication is the church's response to false doctrine or unethical conduct of its members or leaders. It is an official censure in which a person is excluded from communion with the faithful. It's purpose is twofold, first to call the person to repentance, and second, to safeguard the church from being corrupted.