One size doesn't fit all
'One size fits none' is more accurate. I know any shirt marked 'one size fits all' I might as well use as pyjamas. The same goes in just about any area of life you could imagine. That's why there are so many different types of cars, bicycles, shoes, televisions, and microwaves. But somehow, when it comes to computer operating systems, a lot of people seem to miss this small but important fact.
I don't like the idea of a world where Microsoft is the only OS. I also don't like the idea of a world where Linux is the only OS. Because neither Microsoft nor Linux can 'fit' all people.
For some people, Microsoft fits. For some people, Linux fits. For some, it's Mac, Be, BSD, NeXT, OS/2, amiga, or any number of other alternatives. I don't want to shove them into an ill-fitting environment - and I don't want to be shoved into an ill-fitting environment. After all, you wouldn't buy a three-quarter ton pickup for commuting, or a firefly/metro/bug for heavy towing.
Each OS has its strengths and its weaknesses. It's a design decision, really - an OS with high security will have low convenience of use, because everything is protected. An infinitely configurable OS is nice - if you have the time to learn all about the configuration. A homogeneous OS is handy if you want everything to work the same way. The Macintosh, for example, has an incredibly consistent and easy to learn interface, whose basic concepts haven't changed much since it first came out (take a look at screenshots of MacOS1 and MacOS9 side by side. 9 looks a lot nicer, but they both have the basic elements in the same place).
And no, I don't think the world will break down through 'incompatibilities' if everyone uses the OS that suits them the best. Guess what - the web server that's serving this page up to you doesn't care what OS you're running, it just spits out this standard format (HTML) at your IP address using a standard protocol (http). Along the way, it is passed through various routers who also don't care what OS either end is running, and is reassembled at your end, the whole thing being handled by a standard called TCP/IP. Do you get what I'm driving at here? As long as people adhere to open, well documented standards, people can communicate no matter what OS they use.
Now of course this example just touches the internet. Other things like file formats aren't standard (unfortunately), so people are forced to either convert to their preferred format and lose some formatting or switch programs to read shared documents, neither of which are good options.
