Well, the last on this was me pointing out that not being able to take the Attack action (capotal intended) was due to specific prerequisites for that action. Specific limitations on specific actions that the entire table can see and utilize (as a player I can leverage those limitations to prevent attacks on my character -- see "kiting").do not, on any way, make a case for a general power to deny any action on any reason.
A useful tip for arguing is that you can take a general point into the specific, but you can't take a specific point into the general. Here, you can't extrapolate a general rule for denying actions from the specific requirements for a specific action.
So, yeah, your argument holds no water if your basing your assumption of general GM power to disallow actions on an example that hinges on the specific requirements to take the Attack action by making a melee attack.
Did I say specific and general enough? I feel like I did, but also feel like I maybe didn't say it enough to get the point across.