I had this argument with someone a while back. Dumbest fucking argument ever.
Athleticism (height, weight, speed, strength) is one of the biggest factors when determining a player's quality. You cannot take away someone's athleticism just because they were ahead of the curve at the time. LeBron James is one of the fastest 6 foot 8 people you will ever see. He's ahead of the curve. Let's take away his athleticism just because he's more physically gifted than the rest of the NBA and see what player we have.
While we're at it, let's take Babe Ruth out of the "best baseball player of all time" list, and put Carlos Delgado ahead of Ruth. I mean, Ruth was beating up on white pitchers who didn't throw any junk pitches and couldn't hit 90 mph. Delgado hit over 300 homeruns vs. pitchers who could throw upwards to 100 mph and so much junk mixed in. Same exact argument, but it's amazing how stupid the argument sounds, doesn't it?
Wilt Chamberlain was ahead of the game -- that's not a penalty. Of course LeBron, Shaq or Dwight Howard could dominate back in the 1950's, but you're forgetting that they didn't exist in the 1950's. Shaq and Dwight Howard's body composition was built over time through evolution and the help of things such as personal trainers, fitness discoveries, health discoveries, basketball gaming strategy, etc. If you were physically more dominant than 99.99% of people in the world at the time, you are an athletic specimen.
Wilt is easily the second best player in the history of the NBA. Anyone who disagrees should just live in the modern era and not even pay attention to history.
Oh btw, Larry Bird wouldn't be nearly as good if he played now. Players today > historical players