Collateral obligations aren’t stock agnostic at the central clearing level.

The "stock-agnostic way" metric is volatility. GME experienced volatility never seen before. Thus measures never taken before are justified. Given your quotes around "had to" I suspect you don't believe Robinhood was essentially forced into these measures. If you're going to hate Robinhood, it should be because they created a gamified app that emboldened people to jump into the GME debacle and for creating a service that goes down in times of heavy trading, not because they had to take measures to reduce their risk profile.

I am not well versed in the financial services industry but this article seemed to offer at least a plausible explanation for why Robinhood (and other capital limited brokers) stopped buys on GME specifically:

https://stu2b50.dev/posts/why-robinhood-d3580b

I want to be upfront in that I can't verify the accuracy of this article, and I still look askance at Robinhood personally; however, it did pique my interest in keeping an eye out for further analyses of the incident as more details emerge. And it seems like there is plausibility to Robinhood's claims that they had to halt buys.

And...on the face of it, I am all for regulation that places risk management requirements on financial firms.