In all fairness I've never seen anyone kicked in bronze due to levels (taking forever to ready is a different issue). And kicking an underleveled player in gold is a perfectly acceptable.
Silver is an interesting one as its definitely possible to carry low leveled players. I've completed silver a number of time with low level players, a full team is still preferable even if some are low level. Once a guy brand new to the demo ended up adding to our quite handy 3 man team on silver. In a short time he was powered through to level 9 even though he died a fair few times. So I don't tend to kick people on silver, though if I enter a silver lobby and the other three are under level 5 I will just leave the lobby (unless I'm leader and I can knock it down to bronze).
Silver is an interesting one as its definitely possible to carry low leveled players. I've completed silver a number of time with low level players, a full team is still preferable even if some are low level. Once a guy brand new to the demo ended up adding to our quite handy 3 man team on silver. In a short time he was powered through to level 9 even though he died a fair few times. So I don't tend to kick people on silver, though if I enter a silver lobby and the other three are under level 5 I will just leave the lobby (unless I'm leader and I can knock it down to bronze).