Craigslist Inc. v. 3Taps Inc., 942 F.Supp.2d 962 (N.D. Cal. 2013) was a Northern District of California Court case in which the court held that sending a cease-and-desist letter and enacting an IP address block is sufficient notice of online trespassing, which a plaintiff can use to claim a violation of the Computer Fraud and Abuse Act.
For one thing, the extension author is not an active participant and cannot be considered to be trespassing. A user, maybe. But I don't think we'll see Slack banning users anytime soon.
The intent is clear. I don't know the details of those decisions but Blizzard has won cases and stopped people from distributing tools that access their services in ways they don't approve of.
