I rarely engage online, but I did a few months ago after the tv website had just switched to facebook comments, and they covered a bike-car collision (no fatalities). Because they'd just switched to the facebook thing I was able to see that the idiots were in high school. (Knowing that bit of background made a difference in how I viewed the comments.) So I patiently explained that no, the school track is not a viable alternative to highways. Neither is the 3/4 mile bike path in town. How fast the conversation dried up.
But mostly I stay out of it. If I get the least bit upset I get out of there.
2009 Trek 7.2FX WSD, brooks Champion Flyer S, commuter bike