This is a chicken and egg argument.

> Security > Prerequisites

Both of these arguments rest on the assumption that RCS replaces iMessage. That's not the point. The data is already unencrypted. You already need a paid phone number. The benefit is that two large groups of users' devices that interact poorly today interact better with RCS. Google isn't asking Whatsapp or Signal to implement RCS, it doesn't make sense that they'd expect Apple to shut down their proprietary service to use a less-featurefull option instead.