This kind of thing has been a huge problem since the start. It comes with the territory. In the time I've spent being invested in this topic I have not met a single GG supporter who supports doxxing or sending threats to people. We have spent a lot of time trying to discourage these actions in people sympathetic to the cause and trying to distance ourselves from people who do this kind of stuff. But like I said earlier, we lost the image war. There is simply no way GamerGate will ever be viewed as anything but a bunch of evil neckbeards by the general public.

When you have a group of people who are largely anonymous getting into heated conflicts with people who have faces, there are going to be several problems.
First, anyone can attribute anything they feel like to the movement with no evidence because it is so decentralized. You can honestly say pretty much anything you want about "gamergate." It will be your word against theirs, and since we already lost the image war, you're going to be right in the eyes of the public.

Second, it is so easy to undermine or infiltrate a movement like this. All people have to do to "be a part of gamergate" is say that they are a part of gamergate, regardless of whether they actually believe in anything the movement stands for. Anyone can jump in and do a shitty thing, then have that action be attributed to the whole movement.

Sorry, that was a really long-winded, roundabout answer to your question. Basically: Doxxing sucks, it sucks that that happened to Felicia Day, GamerGate does not support that action nor do they support the person who did it. In the end though no one cares what GG has to say about it because they are just evil nerd keyboard-warriors who want to bring down women.

But as long as we're talking about doing shitty things, that is not exclusive to one side of this debate.