One UK airline was getting so fed up with early morning drunks on its flights from a UK regional airport that they hit on an innovative solution. They asked the airport how much profit the bar made at that time of day, then paid them slightly more to close the bar!
Denying boarding to drunks who have checked luggage in the hold will mean delay and disruption for everyone else, including those on later flights for which the aircraft has been scheduled. Not to mention the risk of injury to the gate staff. So it's not surprising that some airlines accept passengers who have had too much to drink before boarding.
If passengers refuse to obey the lawful instructions of cabin staff in flight, then the flight should divert and the passengers should be off-loaded into the hands of the local police - and the whole cost later recovered from the miscreants.