You're absolutely right! The basic software infrastructure that can be adapted to safely and securely handle user data is completely free. It may be worth cons

You're absolutely right! The basic software infrastructure that can be adapted to safely and securely handle user data is completely free. It may be worth considering that adapting said FLOSS software, doing the requisite custom integration work, and then doing a large migration successfully might all be perhaps slightly less free than the software you correctly and wisely point to.