You just don't know whose tapped the line, whose listening, and what systems your text is being indexed into. So reliable E2E is key.
[1] https://theintercept.com/2014/12/13/belgacom-hack-gchq-insid...
Unless you're using physical couriers and airgapped networks with TEMPEST protection. I say this unironically; these are facts people tend to brush away.
The cloud is at the end someone else's computer. No, I'm sure Microsoft CEO isn't interested in sabotaging my business just like I'm sure the POTUS doesn't actively decide to kill innocent civilians. However, they make compromises (something we all do in engineering) and some of those compromises could end up with us as collateral damage.
What I'm getting at is even if all government agencies have purest of pure hearts, someone somewhere will eventually leave a door unlocked. Nobody can tell me with 100% certainty that this won't happen in the US and I trust their competence more than some outside contractor working for the Qatari emir.
This is my point of view on why we shouldn't have a dragnet. I don't have to argue that my government is evil. I don't even have to say my government is incompetent. But who in my government will testify for the other 200+ governments and their agents?