Steam - you need Steam account (also applies to Valve Index then)
iPhone - you need Apple account
Android phones - you need Google account
Oculus before - you needed an Oculus account
The short time during which they required a Facebook account (i.e. an account linked to an unrelated service) was a fuck-up, but they have since reversed that decision. Now it's just a separate standalone VR-related account.
If anything, that is still better than the current Google/Apple situation with their accounts, which link together a bunch of unrelated services (photos, email, payments, storage sync, etc.) in an inseparable way.
Sorry to break it to you bruh, but if Facebook owns the IP, they're harvesting and monetizing the account data, end of.
This includes all of the subsidiaries like Instagram and WhatsApp as well.
Let's also not forget that illegal activity exposes user data in addition to greed, and just the fact that your data is in yet another pot increases your risk. Also yes all corporations are greedy and evil but they're definitely not all equal in how bad they are, and FB is one of the worst
Are you willing to compromise on all of these intrusions into your life? Many people are, but I'm not one.
Ok, so Facebook knows I have a VR headset and bought some games, and they're using that information in targeted advertising (as much as things like EU law allows them where I live)? Quite frankly, I don't care - this doesn't really affect me in any practical sense - and again, thanks to existing laws, I can actually opt out from a large part of it.
From a practical standpoint, I would have a much bigger problem with a situation that exists with Google, where some people had access to their email and other services disabled, because some stupid bot classified their comments in YouTube livestream as spam with basically no recourse until the story blew up in tech news (https://gamerant.com/markiplier-stream-ban-lock-users-out-of-gmail/). The root of the issue there is that those accounts just shouldn't be linked, and what you do on YouTube shouldn't affect your access to your own email etc.
You may argue that this is simply down to the fact that Facebook doesn't have a strong enough market position to get away with such practices, and that they would do it too if they could, but as it stand today, the giants like Google or Apple are far worse. (And with most of these problems, as well as other monopolistic practices of tech giants, regulation can be a large part of the solution.)
You don't actually need an account to use an android phone with Aurora and fdroid
And the index is just a headset, you don't need steam to use it, valve doesn't do walled gardens AFAIK