Greta Christina puts it thusly:
This is not acceptable. We do not shoot people just because we disagree with them.
(read the rest of it for context which makes it better.)
“While we disagree with the Family Research Council on nearly every issue, the debate surrounding the role of religion in the public sphere should be fought with reason and logic, not guns,” said Edwina Rogers, Executive Director. “We absolutely condemn this sort of senseless violence.”
and American Atheists:
American Atheists is saddened to learn about the shooting at the Family Research Council today. Our thoughts are with the security officer who was injured and the other employees who were traumatized.
American Atheists never advocate violence as an answer to disagreements, even with those who believe differently than our members.
I can’t think of anything to add. I don’t like the FRC or what they advocate, but you don’t go around shooting people you disagree with, or otherwise doing or threatening violence. This is not acceptable.