IO does not mean what you think it means.

State.hs

import Control.Monad

data State s a = State (s -> (a, s))

instance Monad (State s) where
  return a =
    State (\s -> (a, s))
  State j >>= f =
    State (\s -> let (a, t) = j s
                     State k = f a
                 in k t)

get ::
  State s s
get =
  State (\s -> (s, s))

-- If it is the case that…
a = liftM (\ a -> [a, a]) getLine
b = sequence [getLine, getLine]
-- demonstrates that "IO is impure" because they are inequivalent programs,

-- then it is the case that…
a' = liftM (\ a -> [a, a]) get
b' = sequence [get, get]
-- demonstrates that "State is impure" because they are inequivalent programs,
-- which is absurd — QEA.

-- They are in fact inequivalent programs regardless.
-- Using IO does not mean you are not doing pure FP any more than using [] does.
-- Abandon this common myth, leaving it to propagation on degenerate mailing lists.