As much as I usually agree with you, Kane, this pretty much proves the point I was trying to make. :)
The problem with those chat channels (and clearly this is a problem more for me than for others) is that I felt as though I was getting far more annoyance than assistance out of them. I grew tired of walking into a city and hearing an abortion argument; it bothered me to try and read between constant RMT-spam and petty, faceless insults thrown carelessly about.
In the end, I left all public channels simply because they are used more for anonymous individuals to vent their insipid thoughts than for any meaningful, or captivated, discussion. If I wanted to try and discuss anything of import, I could find a better audience using the filter of a guild; it's not antisocial as much as it is selective. What is made to be shouted at random to anyone in the vicinity is frequently less articulate and less tailored for specific situations, this is why people screaming things on the street-corner tend to be given a wider berth. :P
Although it may be that FFXIV's essentially one character limit and greater amount of character investment compared to other MMORPGs would temper the degree of unpleasantness in global chat channels. Regardless, I think that the best solution is to just be friendly to anyone you meet unless you have a good reason to withhold your friendship. Ignoring people or refusing to talk in /say only leaves the world hostile and silent - in that respect I agree with most others.