Your remarks only make sense to me if you're trying to remain entirely anonymous on a fetish dating system whilst simultaneously disclosing personally identifying information for reasonable use, and I can't reconcile these two objectives.
At the meta level: I use a variety of online systems that I trust to varying degrees, from high to low. Currently I can control my level of information disclosure by using different email addresses. If these systems now require a verified phone number, I then have to trust them all at 100%, tied to my real identity.
So a SaaS website requiring verified phone numbers seems benign on the surface. However if this becomes widespread then the overall identity landscape is compromised for the user.
At the system level: This is essentially the pseudonym-vs-realname debate. Twitter is the perfect example. Let's say I open an account to whisteblow on my government's nefarious activities. Now if there's a breach or state interception (eg China), they know exactly who I am and where to find me.
Well then this is going to bake your noodle: we also ask for correct name, date of birth, and emergency contact details, because those are also useful/necessary for our business.
Fair enough - your product is clearly operating at a high level of trust. My concern with required verified phone numbers is if they become a widespread pattern, I now need to treat eg my Reddit porno alias as if it is linked to my street address (in case your system and Reddit become compromised).
Back to the context of Twitter, this is mitigating the troll system problem by introducing a user identity one.
