Right now they "force" everyone buying a PC to get Windows, and they're able to do this by unfair OEM licensing schemes and as their position as the monopoly player.
There are so many things wrong with this statement...
1. "unfair OEM licensing schemes"
Really? When did the planet where life is fair blow up and scatter its people across the galaxy and why did so many of them land here?
2. Monopoly player?
So Apple is out of business and no longer selling a Mac? I can't build a PC or order one from Dell without Windows and put Linux on it?
MS has a lot of market share, they don't have a monopoly. I know several people who own Macs.
The meaning of Monopoly, at least in legal terms, appears to have changed from the traditional meaning:
"The only player in the market"
to a somewhat more nuanced:
"The player, or co-operating cartel of players who have such a grip on the market that no other potential (or existing) player can be expected to have a reasonable chance of entering (or effectively participating in) the market".
This does not mean that all potential or existing players in a market should be expected to achieve parity, or be capable of it. What is important is the exclusion of ALL other parties from having the potential to effectively participate in the market. There is also the matter of related markets and the practice of players forming cartels where they essentially carve the larger marketplace up into smaller specializations and agree to split control of them such that each has a market that is "theirs".
As things stand at present, in the desktop market, there are two main commercial players, MS (Windows) and Apple (OSX). Both seem to have slightly different target markets, so aren't really considered to be in direct competition for the most part (when was the last time you heard about Apple trying to get a Mac on every desk in a large company, outside of the creative industries?). There is, however, enough of an overlap (Windows in some creative companies and OSX in an increasing number of homes) that neither can effectively be accused of dividing the market between themselves. This leaves the fight as being essentially between Microsoft and Linux. Granted, Linux is a very fragmented proposition, as competition goes, so you're not really comparing like with like, but it can be argued (and appears that it often has been successfully before the courts) that Microsoft's grip on the market, in particular via its commercial agreements with its OEM partners, has meant that whilst it is POSSIBLE to get a PC without Windows on it, it is sufficiently more difficult to do so, to the extent that they have an unfair commercial advantage over their competitors.
They may not be the only player in town, but to the average user, they might as well be. It is largely for this reason that they are regarded, including by several judiciaries, as monopolists.
Although... IANAL, and this is just my understanding of the matter...