What nonsense, especially if framed in a such an absolutist way leaving no room for nuance. Millions of people are storing their data on self hosted or 3rd party run managed OSS services on multiple platforms. Sure, it is not all perfect, UX might be an issue here and there but compared to having to relearn using some proprietary app redesign every other year because some Product Manager needed a promotion, a lot of OSS stuff is perfectly usable, stable and secure.