See Bruce Perens's explanation: <https://perens.com/2017/06/28/warning-grsecurity-potential-c...>. The short story: adding a penalty to an action that the GPL allows is a restriction of that action, and the GPL does not allow setting additional restrictions. This has not been tested in court, as far as I know.

In the case of Red Hat it is not a penalty (as far as I understand) but a 'bonus' you can keep your support contract when obliging..

My understanding is that Red Hat does allow redistribution so long as you do not infringe on its trademarks. Given that no version of the GPL ever granted trademark rights, this is not an additional restriction, so this is fine.

The same way something like "we can tell you, but then we'll have to kill you" would be against the spirit of the Freedom of Information Act.