Besides miniskirts, it got to the point in tos that pretty much anyone could take over the ship. Hippies? ! How about the crew letting complete strangers just roam the ship freely without any escort? Bad security if you ask me.
Yup. I mentioned this earlier. From memory - I'll probably miss one or more - the following persons invade and take over the ship:
Charlie
Khan et al.
Norman
Redjac
The Kelvans
Sargon et al. (sort of)
Kara from "Spock's Brain" (sort of)
The Klingons in "Day of the Dove" (partial)
The Scalosians
Gorgan and his kids
Commissioner Bele
The hippies
Janice Lester
Add in all the times that the E was paralyzed by all-powerful aliens ("Arena," "Errand," "Squire," "Return of the Archons," "Who Mourns," "Gamesters," "Spectre," "Requiem," "Plato's (implied)," "Savage"), and you really gain an appreciation for episodes where the Enterprise is shown as a force to be reckoned with and NOT something that can be casually seized and controlled. This is why I enjoy episodes like "Friday's Child" and "Obsession" that may not be fan favorites.