There's an extraordinary difference between you being entitled to a company being forced to exist to serve whatever arbitrary need or approach you wish, and there being an open market such that a competitor can set up shop.
If you were entitled to alternatives, that means the tax payer has to reasonably fund every possible alternative that could exist, or at a minimum a vast array of them, and most likely at perpetual losses. It'd be extraordinarily dumb and would become an epic cost for the government and would breed corruption (failed businesses, bleeding vast red ink, perpetually subsidized no matter what they do).
True in the general case - however, it gets strange when that argument is used to defend monopolies, i.e. markets that, for whatever reason, are not open.
E.g., I personally don't see why it's bad when an elected government passes legislation but totally fine when Apple uniterally updates the App Store ToS or Google excludes certain things from Search. In both cases, participants of the respective markets won't have any choice than to comply.
I believe YouTube is comparable. Yes, there are alternatives. However, YouTube's popularity is important for content producers. If you make your own video content and are banned from YouTube, you'll likely have a significantly harder time to be discovered.
I agree with you that this woudn't really be an issue for GitHub, since there is neither a market nor any lock-in effects or monopoly.
You want to participate in web standards groups? You have to use github to do so in any sort of effective fashion.
Same thing for various open-source projects.
The _owner_ of a project has a bit more say in things, though I've heard some people claim that in order to attract contributors a project must be on GitHub nowadays, because many people will fail (or refuse) to participate in any way other than GitHub pull requests.
So I agree with you about Apple and YouTube; I just think GitHub is closer to them than you think it is...
When you cherry pick quotes from the source it sounds contradictory. What I meant, and what I feel was clear when taken in context, is that alternatives exist in this particular case. However if you do not think those alternatives are viable then that's just too bad. You aren't entitled to viable alternatives, or alternatives that fit your definition of viable.
If you were entitled to alternatives, that means the tax payer has to reasonably fund every possible alternative that could exist, or at a minimum a vast array of them, and most likely at perpetual losses. It'd be extraordinarily dumb and would become an epic cost for the government and would breed corruption (failed businesses, bleeding vast red ink, perpetually subsidized no matter what they do).