This makes absolutely no sense. Apple (iOS, OS X as examples) generally is a very closed ecosystem, though not a monopoly, and certainly don't operate under the banner of 'open source'. Google (Android, Chrome as examples) is a pretty open ecosystem, also not a monopoly, and actually is open source, no idea what "banner of 'open source'" means but they just are open source.
On the flip side, there's no reason to hate everything Microsoft do, c# and Mono are great. Maybe people should get over dismissing anything open source that Microsoft do, but the rest of what you've said makes no sense.
Mono is pretty much ostracized from the open source community along with many open source C# projects. Remember the whole ordeal about including Mono in Ubuntu?
On the flip side, there's no reason to hate everything Microsoft do, c# and Mono are great. Maybe people should get over dismissing anything open source that Microsoft do, but the rest of what you've said makes no sense.