We should see CEX.IO's statement and see what they are going to do.
Depending on how that unravels, it wouldn't be a bad idea to DDoS.
But DDoSing or Booting a service wouldn't really call anything in our favor. Bitcoin and other cryptos have a special feature, one that many currencies don't have. People aren't denied to mine, or have it. Nobody can confiscate it.
If we DDoS CEX/GHash just because they're mining, and yes, they might be getting close to 51%, that's still not a excuse to say, "Yeah. They're getting close to doing something dangerous. Let's make a exception." Because if that was the case, I don't think Bitcoin would be were it is now.
We are not talking about denying anyone the ability to mine here. We are talking about ways the community can proactively take action in order to reduce the risk of another market crash. Arguing that taking an action which some people might consider unethical in response to a credible threat to billions of dollars of market capitalization just to protect the interest of a few, mostly anonymous individuals at GHash.io doesn't make any business sense at all. The community has already appealed to GHash.io to voluntarily restrict their mining (as did BTCGuild before them) in order to avoid going over 40%. They made their intentions very clear by their actions and so it is time to consider other options.