Laws are not the only rules, they just have the strongest punishments if broken. Their are social mores and folkways which have weaker punishments if broken; punishments which are dealt out by many other members of society other than the legal system.

To put it another way, being extreme mean, rude, and condescending to and wasting the time of telemarketers isn't illegal either. Yet some are trying to say doing such is wrong, to which I say that the telemarketers have already committed a greater wrong of the same nature.

Many telemarketers are engaged in outright scams. I've listened to many of the recordings referenced by the article, and they're overwhelmingly the same kind of scam.

The basic idea is that they call you up and offer you something for free or at a steep discount. They explain that they need a small holding fee which will be returned to you, then they run off with your money and you never hear from them again. Free solar panels, vacation cruises, driveway sealing, and discount home repairs/weatherization seem to be the common flavors.