That prevents the platform from being abused. Identifying users is one thing, reading their message is another. People can still deny and not answer questions.

That prevents the platform from being abused. Identifying users is one thing, reading their message is another. People can still deny and not answer questions. What matters is the messages being encrypted, identifying users is already being made possible through other means. So yeah, using a phone number is good enough, in my view. There is no perfect security, there is only "good enough" security. Not to mention that phone numbers are more secure, in my view, than other sorts of digital communications, and are not always monitored in all countries.