Earlier quoted context omitted.
Uh, what? How is membership in a website that is known, markets itself, and is designed as a cheating website not evidence of the intentions and motivations of its members? Of course membership in Ashley Madison isn't irrefutable proof that a person is looking for an affair. But how is it also not good reason to believe that he/she is?
You can use a gun for killing, and it's marketed for that specific purpose. Does owning a gun make you a killer?
The reputation, marketing, and design of guns is a good bit more varied than Ashley Madison's. But yes, buying and learning to use a gun shows a certain intention or willingness to kill. It may be to kill a deer you're hunting or to kill a person in self defence, but in general it's evidence of a certain willingness to kill.