Day trading is a massive negative sum game. It is not close to zero sum.
Commissions/fees, slippage and expenses take large amounts out of the game.
As far as competition, of course you are competing against technology and pros with faster execution, better skills and knowledge of the game you do not have.
Nothing close to 40 percent of daily volume comes from what you would consider a day trader. A large portion does come from programs and algos.
There is no way to always not trade against market makers/specialists. However, some situations do attract more "public" money than others.
That is not to say someone can or cannot beat this game. However, I doubt you will.