I think what tptacek means is that when we sign up for a service, we agree to terms of use. Even if we don't sign it, it might be legally undecided as to whether that counts as
a binding contract, nor whether "terminate the user's service" is the only recourse the service provider has.
In most of the world it is decided. The decision is click-wrap 'contracts' are unenforceable. Starting with the fact that they don't meet the definition of a contract.
He talked in detail about how his company is long-time user of Slack. He and his colleagues each agreed to the "no reverse engineering" terms when they signed up.
Maybe the agreement isn't binding depending on his local jurisdiction, but it's unclear how he could use Slack without agreeing (or at least clicking "agree") to the terms.
In many jurisdictions you can't be bound by an agreement if not explicitly agreeing. It most likely boils down to where Gervasio lives. In my country for example I'd be certain Slack would have no standing at all with this. Though even in the US Slack would have to pull an Oracle to win this (which, well, is the risk that they might). Good reminder though in which moral category of enterprises Slack has to be sorted in.
It does not matter, he does not want to fight this.
It might be more than just a EULA. Often to sign up for an API key, you have to go through a bit more explicit agreement to a ToS than there is in a standard funnel. There's also a bit more of an expectation that people will actually read them (and are competent to understand them).
"Terms of Use" are part of the agreement between you and a service provider with regards to the service being provided. That's a civil law contract like any other.
No that's not, and I'm not playing on semantic. Laws are above any terms of use, regardless of what they might say. And not using the product makes you not bound to the terms of use, unlike laws which you have to obey at all times.