Not all lap kids cry. Mine doesn't. I've had compliments. Besides, crying is just as annoying as someone who reclines right in front of me. Or having no food anymore. Or angry FA's.

Annoying, but you can do stuff. Wear noise cancelling headphones. Bring food onboard. Ignore the FA's.

Someone taking up half your seat isn't something you can do to ignore. You can't draw a line like you can with the others. Not all kids cry. Not all FA's are angry a-holes taking it out on passengers. Encroaching is encroaching.