The defeatist mentality from my perspective is arguing that we shouldn't try to make locked down stuff less locked down.

And in many cases, you don't have a choice to use Signal or etc. What if all your contacts are using iMessage? Sure, most of them will have SMS, but that's not guaranteed. There will always be edge cases of users who are locked in due to situations outside of their control. Shouldn't we be trying to make things less locked down for them?