The difference is of law rather than rights.
You have a right to privacy, but it's not absolute. If you are suspected of a crime with reasonable evidence, a search warrant can be obtained to breach your privacy - namely entering your house and looking at all your stuff. If, on entering your house the police find a locked cellar door, they can ask you to hand of the the key. It's not good refusing to hand over the key on the grounds that it's a breach of your privacy.
Now, suppose the police find out you have a safe deposit box at a bank. They can also approach the bank and politely request entry to your safe deposit box, and with the appropriate warrants, the bank will happily open it up.
All of this is quite legal in most countries. In many cases, law enforcement is simply asking to extend this capability to encrypted data, rather than locked rooms and boxes. I have no objection with this, although there are technical issues with it.
Another wholly separate issue is the desire of authorities to decrypt and read communications of people who aren't suspects and haven't been arrested, using much lower barriers than are required for search warrants.This is much more worrying, and rather like saying that everyone should have a new kind of government approved lock on their front door allowing police to walk into any house if they feel they have the need.
It's important to keep these things separate. I have no problem at all with the UK police reading all of Mr Masood's whatsapp messages, any more than I have a problem with them searching his flat and going through his diaries and his sock draw.
What I do have, is a problem with UK police saying that because they want to do this, whatsapp must design a generally available backdoor.
Unlike safe deposit boxes, which can be broken into even if the suspect destroys the only key in existence, encrypted messages often can't be read if the only key in existence is destroyed. That's a technical problem, and it's not the job of private companies to solve the police's technical problems.