GHB aside I wouldn’t even call it particularly dangerous, it’s just blissfully wrongheaded. Ketamine is a dissociative anaesthetic, and it does what it says on the tin: it takes however your mind is at that moment and just brutally lops off all the connections you normally anticipate it having with your body and other bits of itself, with various interesting consequences for mind and body both. Alcohol is alcohol, it’ll depress your euphoria to some extent but it is also in itself sugar and obviously will make you drunk on top of the (significant) remaining effects of the stimulant - rather than calm down, you are far more likely to get outrageously mad and try to punch a stranger, poorly, because already the whole point of abusing most stimulants, euphoria aside, is to turn you into the world’s sharpest spoon.