Can someone tell me why twitch jungle is acceptable?

well actually an adc in jungle is very very easy to invade and kill or counter jungle , they typically are super squishy , have to auto and kite camps til they get to a couple of levels. so just like kog jungle , invade him and live in his jungle and kill him .

and jungle twitch works cuz of his ambush being able to gank with out being seen like eve, shaco ,kha, rengar

I think people are failing to see the big picture here, Twitch doesn't really need farm to snowball, While Lee feeds on his camps, Twitch feeds on his champs. A good JG Twitch will be 10/0 with 20 farm at 10 minutes, Twitch is the super cheese, He shouldn't be this strong, His jungle needs to be hindered.

Because a Twitch ganking a lane is freaking terrifying since he's invisible until he attacks you. Wards don't mean shit early on.

You sorta got it spot on on why its acceptable. The goal of the oppossing team isnt to make sure you have fun its for them to win