It's not just inconsiderate, it is also quite cruel.
Babies get 5 to 10 colds per year. So the odds are pretty good that when you are taking your baby on a flight, they will have a cold. If you have ever flown with a cold, you know this can be incredibly painful. During a flight, the air pressure in the sinuses and middle ear must equilibrate with the cabin pressure inside the airplane, which changes during ascent and descent. Colds, allergies and other conditions can cause blockage in the Eutachin tube (which connects the middle ear to the back of the nose and maintains equal air pressure on both sides of the eardrum). This means the pressure in the sinuses cannot equilibrate. In severe cases the middle ear can fill with fluid, resulting in an ear infection. Or the eardrum can even burst. The pain can be intense. I have had it as an adult and the best way I can describe it is if you imagine someone is trying to push your eyeball out of your head with a knife point from the inside if your head. That is what it feels like. I have sat next to adults in tears due to the pain. Is it any wonder that babies cry on planes?
It is not the child's fault; they shouldn't be in the plane in the first place. It is never the child's decision to fly, it is always an adult that makes that call and you can bet that it is done for selfish reasons. Babies should not be taken on planes. Not because they may inconvenience other passengers, but because there is a good chance it will be very painful for the child. What kind of parent willingly puts their child through that?