Arsenal supporters: why are you afraid Cesc will leave us for barca?

Why would they want him last season apart from a few good games he was as good as useless... he under performed for two thirds of the season ... all this adulation of Cesc gets on my wick ... yes he has the potential to be world cl but of yet isn't' consistent enough and all you hear is Arsenal Fans what if Cesc goes... well, tell you what give me 20 -30 million and he's yours who would he displace at Barca then??? nobody is the answer