Especially in the world we live in right now - email and other work-hosted communications platforms are not a resource provided by work, they are the WORKPLACE.
I think I disagree. This is exactly the role of the government to adjudicate. I would suggest a standard something like "everything is allowed, unless the company can prove significant harm". So instead of the gov saying "email is ok!" you just get to use email, and then the company has to go to the gov and prove that you using email is a drain on their resources in order to fire you.
That said, even if it is detectible, I think that employees should be allowed to drain some small amount of a company's resources to organize. I am allowed to use company resources for emails like "who wants to go for beers after work?" why should I not be allowed to send "who wants to go organize collective action after work?"