At SFO there is something called the "free speech booth." The sign above it should read: "Abandon all Relevance, Ye Who Speak Here."
We are suffering from a similar problem. Too much of the speech in public places on our campus is simply not a dialogue. It is strangers from the university community who visit to make anti-Semitic rants and similar nonsense (see e.g. Phillip Garrido ). This activity cheapens the atmosphere and makes any speaker likely to be ignored or heckled as the newest crank in the public square.
What to do about it is a difficult matter. One simple step involves our sorry sartorial state. I don't take people in pajamas seriously (most of the time), but so many of us think it appropriate to wear our uggs or our sandals in public. If we want to be taken seriously, we could start by dressing the part.