Filter me this

How is it that by my son's age, my sister and I had developed such refined filters. By nine we definitely thought before we spoke. Our main objective when speaking with relatives was not to offend anyone in the family and to preserve a sense of harmony. This was instilled us so strongly, yet my parents' childrearing style was so loose and liberal. We never got spanked or punished, but we were very polite and thought carefully about what we say and how we behave. My son, on the other hand, has a very feeble filter, if I can even call it a filter. He doesn't have much of a concept of how others may perceive what he says. Two examples from today:

I was driving all three of my kids in a highly unreliable car. He knows the car has issues and is a little sketchy to drive. The baby was starting to cry, and my almost-two-year-old was starting to whine and scream in irritation as well, which always makes me frantic behind the wheel. When I started singing "If You're Happy and You Know It," he corrected me, saying there is only one way to sing the song in correct order. I responded that pretty much anything can be inserted in the blank in the song, sort of like in the game Simon Says. And then my son joked about how he could insert a line that says to crash the car. Yikes! How would he not realize that's not a funny, but a stress-inducing thing to even put out there.

The other example from today would be that when he found a basketball on his bed which I had given to him as a surprise present, he immediately questioned whether it was new because of discoloration he had noticed on it. He argued that the ball must be used which irked me mainly because he kept arguing and not listening to what I knew to be true, and what he said seemed judgmental, like he wasn't appreciating the present.

How can it be that his politeness filter is so underdeveloped when I constantly model empathy and when we talk about impact of words and actions quite a bit. Is he just not very emotionally mature? Is it the larger societal context in which he is growing up? I just don't understand.