If I donate my time to a soup kitchen I am not threatening the sandwich shop. And my letters to the editors do not threaten the daily columnists.
Competition is an aid to an industry.
Given that the competition is voluntary, and not an artificial product of a court ruling, it can only be a benefit. It is not in competition with closed source software anymore. That Open Source has become a significant enough factor to make Jim Allchin sweat is an indicator that least certain sectors of the closed source market are obsolete. The profession of scribe used to be a lucrative trade. But the invention of the printing press vastly lowered the producing copies of books.