I don't mind what the default is when I install a browser since I know to change it, but I have issues with any piece of software altering the settings of another unrelated piece of software that I've already configured.

I'm not OK with software messing with my other software.

I install Office because I need it, not because I think it and everything else Microsoft has made is the best thing ever.

Lets not pretend browsers are like other software. They are essentially a VM that can run remote untrusted code.

Software has changed the start page, search providers, and installed plugins into browsers for a very long time, this is nothing new.

How many users are going to get "stuck" because of the text below, from the MS bulletin?

"Once this feature has rolled out, your end users can change their search engine preferences only via the toggle in the extension; they cannot modify the default search engine in browser preferences."