This is not about preventing you from doing that, it is about preventing services with many users from providing that service to you without a backdoor.
You can just send anyone you want an encrypted e-mail or message, but Signal can't facilitate that without the required provisions set out in those laws. If these dumb laws get enacted, Signal cannot get away with just pretending you are sending gibberish whilst providing true end-to-end encryption without any client-side scanning or whatever to you, but you are well within your rights do so yourself on top of Signal (if that's even possible); they just can't provide an automated means to do that for you.
You can just send anyone you want an encrypted e-mail or message, but Signal can't facilitate that without the required provisions set out in those laws. If these dumb laws get enacted, Signal cannot get away with just pretending you are sending gibberish whilst providing true end-to-end encryption without any client-side scanning or whatever to you, but you are well within your rights do so yourself on top of Signal (if that's even possible); they just can't provide an automated means to do that for you.