I think there is a relatively well-defined, if somewhat broad, line that borders between free speech and harassment.
For example, suppose that I were to write a couple of articles saying what a bad, unreliable programmer you were. Any time someone asked me what I thought of your programming skills, I would tell them that they're lousy and no one should hire you. Further, I go on to Twitter, Google+, HN, and Facebook and make a few comments about what a bad experience I had working with you. Maybe some of the people I know also know you.
In my understanding, that scenario isn't harassment but it is free speech. I'm not making direct personal attacks against you and I'm not threatening you, although I'm not saying great things about you. There might be a case for civil libel there, but it would be a tough argument and would most likely need to be solved in court via lawsuit.
Now lets take that scenario further. I think you're a shitty, horrible human being. Not only do I write a couple of articles about what a bad programmer you are, I go on to talk about how anyone that knows you should kick you in the ass or push you in front of a car. I start finding out background info like where you live, who your family is, what your phone number is. I start giving out all of your personal information. I start calling your house at odd hours, breathing heavy, and hanging up. I do that 20x a night for weeks on end. You change your number. I find out what your new one is. On Twitter, I create hundreds of fake accounts and send you DM's and @'s with some really awful messages. I start dropping indirect hints that I think you deserve to die. I do the same thing anywhere I can find you online.
Now in that 2nd, really fucked up scenario, that's harassment. I get arrested and my lawyer claims that was my free speech. Total bullshit.
So when I say I believe there's a well-defined but broad line it encompasses those two extremes.
I believe the big defining difference is that if I say or do something to you, that's personal. If I say something about you, it leans towards public. There's of course all kinds of ways I can say stuff about you and have it be very personal though.
So I think that issues like this are going to often be on a case-by-case basis because it can cover a range of scenarios. I might say something about you that you feel is harassment while to any 3rd party observer its obviously free speech, and vice-versa.