As non-lawyers, both the author of this article and most of the commenters profoundly misunderstand the implications of this decision. True threats of violence were not protected by the 1st Amendment before this opinion was issued. True threats are still not protected by the 1st Amendment now.
The only change is the mens rea (state of mind) that a prosecutor must prove to convict. It is now a subjective standard (recklessness) rather than an objective standard (whether a reasonable person would have found the messages threatening). This article makes no attempt to discuss or clarify this distinction.
And the decision is unlikely to change things on the ground in a typical prosecution, including in this very case. Although Counterman's conviction was overturned, he will almost certainly be convicted again when retried. His hundreds of disturbing Facebook messages to the victim using multiple accounts are truly threatening under any mens rea standard.
Likewise, prosecutors would have no trouble obtaining convictions regarding the other victim mentioned in the article, Mr. Tomlinson, including for harassment, stalking, and identity theft, among other likely charges.
Bottom line, there are many challenges in bringing cases against online harassers (e.g., merely finding the perpetrators in the first place can be difficult). But changing the mens rea standard from objective to subjective is not one of them.
And, contrary to many of the comments here, this case was clearly NOT about conservative vs. liberal judges. Justice Kagan wrote the opinion of the court, joined by Justice Jackson. Justice Sotomayor would have gone even further, requiring actual intent (a conscious desire to make a true threat) rather than just recklessness. And the only two who would have retained the current standard are Justices Barrett and Thomas, the most conservative judge on the court.
There are plenty of other cases that highlight the conservative/liberal split. This is not one of them.