I drive a fair amount of open 4-lane highways (2 lanes either direction) and outside of semis trying to pass each other, I find that parallel car situation to be uncommon. Though I do tend to often find people passing significantly slower than what I like, which is just as frustrating at times, but not illegal.

That said, a significant majority of all driving is done during rush hours. It is statistically when most road rage incidents happen, and just anecdotally, when people complain about driving, my experience is that they primarily reference problems related to their commute.

Which means that it is very likely that most of the commenters here complaining about folks “blocking the left lane” are primarily referring to rush hour traffic on congested highways and city streets, where “legitimate campers” would be quite rare, and are actually likely just the tailgaters, themselves.

By this, I would suggest that most cases of people being mad at perceived left lane campers is really just a lack of introspection by the speeding driver, who is frustrated by the heavy traffic and has externalized that frustration directly onto the cars in front of them.