If they EU wants to spend trillions of euros and send millions of europeans soldiers to fight for zelensky then they have every right to do so. If they don't want to pay that price then they should shut up.
There's no talk of sending European soldiers to fight for Zelensky, the only thing currently being discussed is a peace-keeping force, once an accord is reached. If that happens there will most likely be elections held and Zelensky might not get a second term, or maybe he will?