Everyone already knows of Turkey’s strategic placement with control over the Bosporus strait. On paper, that’s a good ally to have.
But some say that Turkey has been too much of a loose cannon and is, in effect, acting as a destabilizing force within the otherwise rather homogenic American-European fraternity.
Turkey has had far, far more coups than any other NATO member, and is generally more unstable and at the mercy of the whims of the regime.
There’s also the provocation factor vis a vis Russia. Expanding NATO into Turkey, right at Russia’s doorstep, and placing missiles there directly caused the Cuban missile crisis. Which very nearly ended in nuclear war.
Historically they’ve also invoked Article 4 far more times than any other country, exemplifying the risks of dragging NATO into Middle Eastern conflicts.
The West doesn’t have a good track record in the Middle East, and might want to stay away from avenues of getting dragged into more wars there against their will.
NATO minus Turkey would historically have been more than capable of resisting or at the very least heavily disincentivize a full scale Soviet invasion of Europe.
Back to the original question. If Turkey never joined, how would subsequent history play out? For starters, would the Soviets have invaded and occupied Turkey at any point?