^^^This
I was ganged up on by my brother, stepdad and stepsister's other half last weekend, on just such an argument. My stepdad had apparently taken a couple of roadies to task for using the road instead of the pedestrian/cycle bridge, which the council put in "at great expense", and wasn't interested in me suggesting that maybe he should just slow down a bit. Cue the usual stuff about "facilities being provided out of my taxes", "cycles should be banned from the road because there are more cars than bikes, that's democracy", "one day you'll get yourself killed and you should think about the poor motorist who ends up hitting you". I kid you not. My brother started it, and I should have known better than to rise to the bait. They probably think it was just a friendly argument, that I know they didn't mean it, etc.
From strangers, the combination of rightous indignation, a misplaced sense of entitlement and complele lack of a clue is what grates. On top of that when your own family won't back you up... bah.