The solution would be to disallow this feature, not to stop trading of certain tickets on all accounts, most of which are seasoned and funded
Full explanation with math here: https://twitter.com/kralctrebor/status/1354952686165225478?s...
Also, it’s not realistic to expect them to completely retool their entire app and infrastructure in a matter of hours to disallow margin-based trades of only certain securities. If this was a long-term concern I’m sure they’d do exactly what you suggested. However, this even ramped up in only a couple of days. Let’s be realistic about what they can re-engineer, test, and deploy to end users in that timeframe.
If I'm reading the Twitter thread right, what killed Robinhood was the component of ">30% of your flow is in one stock", which is something that I could absolutely see never having happened to Robinhood until now.
They do have the ability to change the margin requirements for a particular stock, as well as disable “instant deposits”. They don’t let you withdrawal money until it’s cleared so adding the ability to hold the funds in the account until they clear wouldn’t be hard if it’s not already there.