I honestly don't see the connection. How would limiting free speech online deter terrorism? What kind of limitations are you talking about?
Are you advocating that we eliminate all anonymity in online speech?
Are you suggesting that we should prohibit speech on certain topics?
Are you considering that expressing certain viewpoints should be criminal?
I think any of the above are terrible ideas - see John Stuart Mill at
http://www.csulb.edu/~jvancamp/free/Mill_w.html - but if you come up with some other proposal I would be happy to consider it.