Has anyone (with tons of money to spend) ever made a suggestion to you that they might sue you? It is pretty stressful. I do not recommend it to anyone.
This is the difference between fantasizing about the likelihood of outcomes when you have no skin in the game and being on the other side of a well funded adversary that is threatening a lawsuit. Put yourself in the POV of the one with skin in the game and consider that it may take years and insane expense (time/money/energy) to prevail against even a poorly founded lawsuit.
Being "right", sometimes, is not worth the fight.
Adblockers inject code into sites. So do password keepers. If sites could sue adblockers because it breaks their terms of service, don't you think they would?
You are not bound by the slack terms of service except in the scope of your slack account or an API connection of some type.
Someone else can use my software all day long to break their terms of service, but that doesn't make me liable. I didn't agree to anything.
People need to realize that terms of service are a civil contract. It's not "illegal" to break them. Especially if you didn't agree to the terms.