[devit]

Transactions have to be irreversible so that law enforcement is impossible, which is the main selling point of cryptocurrencies.

Of course that's a downside if you are the one who would like law enforcement to happen (either because you are the victim of a theft or you want to enforce on others).

Also fraud can be done with reversible transactions as well, in particular the reversal can be fraudulent; in general, reversible transactions are only really effective if the conveyance of whatever was paid for is also reversible.

[Nursie]

Reversible transactions are effective at building trust in situations where you don’t trust the merchant.

If I can reverse a transaction if I get ripped off, I might consider using a smaller or newer vendor. If I can’t then no chance, I’m sticking to the one I trust, even if they don’t have what I want.

Reversible payment methods are a huge boon to merchants, whether they realise it or not.

[linspace]

I thought that the selling point was avoiding centralization. I suppose some measures could be implemented to avoid robbery.