In addition to what everyone else here is saying (this is the most mind-bogglingly stupid idea you could imagine, which will instantly kill the adoption of Signal in the US) I want to point out that the purported reasons for removing this feature would be completely solved by hiding SMS behind a setting. If you want to be EVEN MORE paranoid you could periodically warn users if this setting is enabled, just like they periodically bug you about your pin. The only explanation I can have for this decision is that the real reasons for it have nothing to do with those given.