The /enter idea just makes it even more confusing for new players. You remove convenience for everyone, not just the players who are abusing.
There's also a negative side effect to disabling GTA's doors. Casino's are permanently disabled when the door markers are disabled, all interior cross-links would have to be added to the script, then all internal scripts would have to be manually loaded and last but not least we won't have enex markers that new players will be used to using.