If a broker that handles a very large portion of retail trades suddenly blocks purchasing a security that retail trading has driven the price up then it stops retail pressure and the stock price will obviously drop.... you could say Robinhood cost retail money by removing the upward pressure on the stock. The SEC report on the incident mentions the price rise was mostly due to retail FOMO, and not the suspected short squeeze that got the early folks attention.

A laymen would look at what Robinhood did and think Robinhood cut the fuse to the short squeeze bomb.

The problem with this analysis is that Robinhood didn't choose to block buy orders, they were forced to because they were no longer able to fulfill them. You can argue about whether Robinhood should've been better prepared for the volatility that arose (and that could be an interesting conversation by itself), but they weren't. GP claims "they shouldn't have done it", but continuing wasn't an option. The only other choice they had was to suspend trading in GME all together (both buy and sell orders), but I don't see how that wasn't strictly worse for them and their clients.

it might have made robinhood look better to uninformed retail traders if they disabled both the sell button as well as the buy button.

No it wouldn't have. People who knew they could sell in theory and couldn't in practice would complain to and maybe sue for damages (justified or not) the correct option would have been to let users "lend" robinhood the money for 2 days to process the transaction and have this be explained in the interface.

> the correct option would have been to let users "lend" robinhood the money for 2 days to process the transaction and have this be explained in the interface

As explained elsewhere in this thread, regulations don't allow this.