I don't think it's as frivolous as you're making it out to be. By restricting the legitimate availability of the software it limits the use of it by entities more accountable than the average individual. Companies and governments themselves that use Signal will either be cut off from using the service or swallow the risk of using software they've circumvented controls in order to keep using. The likely result is that suddenly those companies and governments have a tangible motivation to pressure the UK (etc) to knock this shit off. It also sets a precedent for vendors of encryption-dependent software. Imagine if your bank followed suit and pulled out of the UK, arguing that eliminating the reliability and security of online banking would put their customers in danger? All of the above sounds pretty "effective" to me.