Did you not read the tweet or are you just trying to misrepresent her argument? She is asking why different sets of trading rules are apply to retail and institutional investors. If retail can sell, but can't buy, who are they selling to?

"We now need to know more about @RobinhoodApp’s decision to block retail investors from purchasing stock while hedge funds are freely able to trade the stock as they see fit."

Does she or doesn't she say that the retail services allowing sales but freezing purchases are especially worth of investigation, compared to the general category of retail services freezing stock purchases?

Of course, in reality, the only services freezing stock purchases are those allowing sales but freezing purchases. Because freezing sales in addtion to purchases would be much more problematic, not less.

Your comment is not a gotcha. She'd clearly prefer that stock trading not be frozen at all. Freezing purchases but not sales is a gift to short sellers because retail investors can only lower the price, which will induce more people to panic sell.

So the hypothetical broker that had frozen both would be less worth of investigation?

No, I think she would prefer that exchanges didn't restrict purely in an effort to "protect" retail investors and nakedly do the bidding to protect larger institutional investors who are getting squeezed.

A brokerage NOT allowing buys, sells, margins, options on a security is well within their right to do so. It's only when they start to take positions that limit an investor's ability to manage their own risk that it gets a little fishy...

So if you have shares in a brokerage account you think the broker is within his right to prevent you from selling them?

That is not what that tweet is saying. She is saying that particular pattern, sales allowed but purchases are restricted, is especially deserving of an investigation.

I don't know. If they had restricted sales I think that would be much worse. That particular pattern is the only pattern that could exist in practice.