Most Cryptocurrencies do NOT fulfil the definition of a security because there is no underlying "thing". This is why shares (with a company underlying them) are and bonds (with debt and debtors under them) are securities (that and the fact they can be traded) but currencies are NOT. Obviously there are exceptions to that like tokenised stocks. This is also why I would not consider most crypto an investment: there is no source for a reasonable expectation of a return.

In the UK, we just designate certain markets as "regulated" (stocks for instance) and others as not (eg FX). That would avoid this whole nonsense where the SEC etc have to argue that some things ARE securities and others are NOT (if bitcoin is a security then stamps definitely are, do the SEC want to regulate stamps? Or Baseball cards or cars, the examples are pretty endless...).

Watching all of this makes me think regulators either being disingenuous or dumb. I doubt it's the latter. So is this someone just grabbing power for its own sake ("I can get more salary and a better office if we get to regulate crypto)? Or maybe trying to get media coverage to up their personal brand for a political career? Either way, if congress wants the SEC to do this, they should pass such a law, and if they haven't then the SEC should be careful what it sticks it's nose into not least because regulating all of Crypto would be exceedingly difficult and error prone.