This is misinformation. It refers to the reporting message feature that can be misused, and comes down not to WhatsApp having a backdoor, but your recipient not being trustworthy.
Agreed. It's essentially the same as someone showing their phone, with the conversation on screen, to a third party. Now, one can argue whether such "moderation" tools are something we wantatall, as a society, legally, but as it stands it's pretty reasonable for facebook to have it implemented this way.
Reporting is a good feature, as it puts the onus of moderation on society self, and not a centralised authority. Group chats, however, can be reviewed by the WhatsApp admins. Atleast one to one chats are safe.