The world is already migrating to post-quantum schemes. SSH clients warn when a server can't negotiate one. Browsers are defaulting to post-quantum TLS where available.
Jonas Nick of Blockstream Rese...
No the reason to leave bitcoin 'unsecured' as you put it is because there is no credible threat from quantum at all. When (if) quantum ever produces any kind of practical useful result coupled with any kind of evidence of scalability then perhaps we should start worrying about what compromises we need to make bitcoin. While state of the art quantum can't even factor the number 21 without knowing the answer first I don't think we have any reason to worry.