Unless I'm mistaken, any application can read the device's SMS database if given the appropriate permission (and few users are very discerning with regards to permissions).
To an end-user, WhatsApp is essentially an SMS application, except it doesn't use SMSs. Given that, this doesn't seem like the end of the world.
WhatsApp claims to keep your texts secret, and this is a big selling point. They make privacy claims that go beyond normal SMS messages, and that's why this is a big deal.
I've been using WhatsApp for years and seen many selling points, but security has never been one. A link would help because I've never gotten the impression that they were trying to sell security.
huh? Stop making shit up. None of what you said is true. They were sending messages in plaintext not that long ago. Their switch to encrypted communication was merely a footnote.
To an end-user, WhatsApp is essentially an SMS application, except it doesn't use SMSs. Given that, this doesn't seem like the end of the world.