Ehh, why take it so personally, its happened to me for the same reasons I assume, its just their loss
Because it can be a pain to get into games with and against human players and to then be kicked because somebody wants a friend to play is annoying at the very least.
If your friend wants to join a game, back out and add them to your fireteam and join a new game.
And if the host has a bad connection leave the game; it's his game and you're kicking him because you can't connect to it properly.