I have been following the ReactOS debate long before Microsoft's Axel Rietschin wrote in Quora that ReactOS is "a ripoff of the Windows Research Kernel…"
My experience goes back to the days when I was using Lifeboat Associates' distribution of Tim Paterson's 86-DOS and before that Gary Kildall's CP/M on S-100 machines and that was before Bill Gates purchased 86-DOS from Paterson for a pittance which he then used as the basis of MS-DOS. It was the unfairness of that deal that has made me extremely wary or Microsoft ever since—it was wariness past decades since then have taught me was the right stance to take.
I would also point out I have no direct allegiance to ReactOS per se except that I've tested it on multiple occasions and found it quite unsatisfactory (unfortunately), in fact over the years I've dubbed it "The Going Nowhere OS".
I have no comment about whether ReactOS is a 'ripoff' of Windows or not as I'm not acquainted with the facts. I would suggest however that Axel Rietschin use the word "ripoff" with great care given that he's working for Microsoft—he should take heed of the old quip about "glasshouses" and "stones". I would however excuse his exuberance if he's young enough to be a victim of air-brushed history which large corporations are so good at creating.
The key issue that everyone has essentially missed is why this seemingly foolhardy attempt to recreate Windows was attempted in the first place and I'd suggest that it has its roots in the failure of government to uphold existing US Antitrust Law which has a long history back to the Sherman Antitrust Act of 1890. Especially from the Reagan era onward, administrations have failed spectacularly to stop the growth of digital-era monopolies let alone extend Antitrust Law with much-needed extensions that befit the digital era. (It's been clear for years that not only should Antitrust Law be modernized for the digital era but also the changes must be of a degree of sophistication that will make them effective rather than just being a paper tiger).
I don't have the time here to develop all the arguments and go into all the ins and outs about why Microsoft and its Windows monopoly happened and why ultimately the monopoly is a disaster for both users and computing generally so I'll attempt to use a crude analogy to illustrate my point.
Let's pretend that in the 1800s a potential railroad owner had managed to patent the standard rail gauge but either because of ineffective patent law or that government failed to police existing law the patent owner was not obliged to license the technology to his competitors for reasonable fees (or that he refused to issue licenses altogether).
He now has an effective monopoly and investors say whoopee and they invest sufficient capital to build a dozen railroads that span the US from east to west which are sufficiently separated north to south to cover 90% of the country.
In the meantime, his competitors complain to Congress and Congress realizes the error its ways and changes the law to force the patent owner to license the technology for reasonable rates. Meantime, the monopoly has been effective so his competitors are unable to raise the funds as investors believe that the ROI on the remaining 10% will be too small and thus the venture is too risky an investment—especially given the huge initial cost to get the project started (an amount that was fine for the patent owner who had the whole country at his disposal but far too risky for latecomers). The outcome: the monopoly remains in place and the final 10% of the country remains unserved.
Now consider the case when Congress doesn't amend the patent law and 10% of the country still wants its railroad coverage. Anarchy breaks out and each little town defies the law and builds local railways in defiance. In the grand schema of railroad coverage of the US, this hardly matters but many are mighty pissed off that their government has let them down. One of the consequences is that once law-abiding citizens lose respect for laws and law-makers and ultimately the rule of law generally.
When the law breaks down either through existing law being not enforced or through inadequate law—especially when the reason for government taking no action is because of the effective lobbying of monopolists—then you cannot blame the citizenry for taking the law into its own hands (after all, government governs only by content of the citizenry as Thoreau aptly explains in his famous 1848 essay "On the Duty of Civil Disobedience").
You only have to look around you at the world today to know "ethics" and "government" are incongruous words and have been on a collision course for decades. In these circumstances I can only encourage the ReactOS team to continue what they are doing and damn the consequences. (As it seems to me things will only get worse before we come to our senses, so let's get it over with.)