BTC is not, itself, a security. However, there are people creating and buying and selling items packaged as securities in which the underlying business is BTC-based. They trade on what are purported to be "stock exchanges." Some of these are outright Ponzi scams.
Similarly, BTC is not, itself, a Ponzi scam. However, Ponzi scams exist in which the underlying currency is BTC.
If nothing else, some of these highly questionable products look like some kind of commodities future.
This is precisely the issue. You only need to take a quick glance at some of the "Project Development" posts to realize that people are acting and planning to act as broker/dealers, unregistered exchanges, fund managers... the list goes on. What these people are doing is simply illegal, and in many instances criminal.
Many of them are hiding behind some halfhearted belief that they are immune from enforcement so long as they are dealing in bitcoin. While there may be some truth to that as a practical matter, it is becoming less and less true as the stakes become higher and the authorities catch on.
Right now, as I type and you read, the SEC and DOJ are investigating many of these people and building their cases. They won't know about it until it's too late.
This isn't a "risk-averse securities lawyer" thing. This is a no-brainer lawyer thing.