Two words disprove that: Marla McGivers.
She was not doing anything illegal as a crew member. She happened to become under the influence of Khan. Then she repented (saving Kirk) but decided to stay with Khan.
Now you're just making excuses.
In fact during the original Star Trek we saw bigots and fools of several varieties serve aboard the Enterprise. There was nothing "un-Star Trek" about Beckwith; the problems which resulted in the major rewrites to the script were structural and budgetary.
Hell, Starfleet was full of weirdoes, creeps and opportunists. Besides McGivers, who betrayed her oath and shipmates so she can have a historical Harlequin romance, there was Captain Ronald Tracey.
"One of the most experienced captains in Starfleet" who let his crew riot and die in orbit while he waited it out, safe and sound, on the planet's surface. He violated the sacred Prime Directive, murdering the "savages" with his "firebox." All of this because he wanted to the key to immortality ... and profit.
Compared to Tracey, Beckwith was a more upstanding member of Starfleet.
EDIT: And did I mention Rodenberry created Tracey.
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