I’m all for discrediting Facebook services for better alternatives, but Whatsapp employs End to End encryption by default, while SMS is readable from your ISP and anyone intercepting your conversation.
Facebook makes money selling data for advertising. They don’t host and maintain what’s app for the good of mankind. every single thing you send on the app is being harvested for data and you know it. It is decrypted at each end and hovered up for sale to the highest bidder.
Facebook makes money mainly from advertising, yes, which can be done also on Whatsapp and will be in the future.
While they can still harvest some data from Whatsapp even if conversations are encrypted, my point was that they have no way to read the content of messages you send.