[leijurv]

I've heard the metaphor that "writing your ledgers in pen instead of pencil doesn't make transactions irreversible" - meaning that in the same sense, actions on the blockchain could be coded to be irreversible.

The difference is in the authority of who gets to reverse transactions. For example, Tether can freeze and generally arbitrarily control USDT token. USDT therefore isn't really a cryptocurrency, since now a central authority can seize it. It seems to me that this authority undermines why one might want to use crypto in the first place. I don't think you can have it both ways.

[syzygyhack]

It may undermine why you want to use USDT. I don't see why it would affect your desire to use DAI, for example.

The point is that you can have it any way you like it. There are no hard and fast rules like "irrevocability" as described above.

You can have a contract be not updateable, final, and verify its source code to know there are no malicious functions. Or you can have one that is updateable by its developer. Or one that is updateable by an elected authority. Or updateable by a DAO of the contract's users. There's no single way to do it or perfect solution.

Like most software development, it is the understanding of application requirements and selection of tradeoffs.