Given the same theorem, the community benefits from a simple proof over a complicated proof. Program committees look for hard results so if they see a very simple proof, it can count against you.
You need to play the game. If you have many results depending on the situation, you can either split the paper or highlight one result and bury the others. It's a bit unethical to use a hard proof where you know an easy one but many people make an easy proof look harder by adding an unnecessary level of detail or proving a more general but less interesting theorem.
You do what you need to do, within ethical standards, to get your paper accepted. After you get it accepted, remember you have a rewrite for a proceedings version to get the paper written the way it should.