As was proved with Shannon, a €10 tax (passed on to passengers) could be the difference between whether an airline makes a profit or loss on a route.
You're stating your opinion as a fact. I'd see it differently; Ryanair was operating unprofitable routes which were on borrowed time anyway, and when the tax came along it was a great excuse to use to throw their toys out of the pram. And yes, that's opinion too.
Compared to Heathrow or Paris-CDG maybe, but you're comparing an airport with a throughput of circa 18 million a year with airports that have a throughput of 50 million+ a year.
I don't think passenger throughput is really relevant to this discussion -- but if you insist, I'd have thought economies of scale would mean that an airport handling fifty million passengers per year should really be charging *less* per passenger than one handling eighteen million, wouldn't you agree?