Trolls it seems, find pleasure in harming others, and the anonymity of the Internet lets them do so without the fear of being reprimanded or discovered. Remember that Ethan Hawke movie The Purge about a future where for 12 hours out of the year all crime is legalized and murderers and psychos can do whatever they want? Basically the Internet is like that, except all the time.
The people who are really hurt from this study are the ones who use Internet comment sections for thoughtful discussion and debate. Unfortunately, they're often overshadowed by their psychopathic counterparts. The study tries to redeem the other spectrum of commenters by concluding that “Enjoyment of other online activities, such as chatting and debating, was unrelated to sadism.” By the way, they're talking about you guys, because you guys are the best. (Time)