Not necessarily violence, transaction happening in a public place with oversight poses risk of being exposed/caught, which could be enough to deter the counterparty from running away with goods or money, scammers tend to go for easier targets, but yes, physical measures including violence are an option with cash, while electronic one-sided irreversible pseudonymous transactions mostly eliminate those options.

The point is that the threat model of Bitcoin is quite different from that of cash.

That’s a property of how you use it. You can use cash in private, or even without being anywhere near the recipient (for example, by mailing it). You can carry out a Bitcoin transaction while next to the recipient in public if you want.

This is another example of how people don’t think of it properly. Sending Bitcoin to some stranger online is basically equivalent to mailing them cash (minus the chance of having the letter stolen). Most of us would understand that mailing cash to a stranger is probably a bad idea, but Bitcoin is used differently.