I think it boils down to that it doesn't matter what they promise, if you send a videocap of all you ever do on your computer to some company on the internet, you just have to take your chances. Would you put mics and cameras in all of your rooms in your home that send data to Apple (or someone else) to analyze "for your benefit" even if they say and promise they won't do anything bad with the feeds?

At least with gmail and chat clients etc. things are somewhat put in compartments, one of the services might screw up and do something with your emails but your Messenger or WhatsApp chats are not affected by that, or vice versa. But when you bake it into the OS (laptop or phone) you're IMHO taking a much bigger risk, no matter what the intentions are.