No that’s not true.
Please watch the WC3 cutscene again.
The Alliance did not reject the Forsaken.
We never even had the chance to.
It was an Alliance army, not orcs, trolls, nor tauren, that helped Sylvanas retake UC.
Then she killed them all for no real reason (Like Saurfang. She’s a bad girl.)
Yes their leader was a racist a$$hole. But that’s not justification enough for what happened.
If diplomacy had prevailed, she would have been named the regent of Lordaeron and honored as a monarch.