iMessage is just too risky.

Reason is that it is also an interface for SMS, and SMS in Brazil is obscenely crazy expensive, some operators might charge 1 BRL per message or stuff like that (for context: 1 BRL is the price of a cup of coffee or of a bottle of water), using iMessage and having it to switch to SMS without you noticing can rack bills that are easily bigger than your wages.

It's not only expensive, SMS is dangerous too! There is huge amount of fraud around SMS and the “SIM swap” technique to clone credit cards and cause all kinds of havoc, some of them with the participation of corrupted employees from telecom companies.

There’s a toggle to disable send as sms in the settings.

Of course not everyone knows that and it isn’t the default so I can see how this is a deterrent in practice.

You're right, I must have activated that toggle years ago and forgotten about it. Yes the SMS fallback could be painful if you're not paying attention.