As far as I know, there are no specific guidelines on what airports can charge for or how much. Having said that, most seem to benchmark themselves against each other in the same region depending upon what type of services and facilities are available.
As for your mates at YKOW, they probably have not sought or been given any advice on how to achieive the required level of security in accordance with their TSP. Hence, they think the gate has to be padlocked at all times and it has to be one of them that opens it.
As for stopping your aircraft from departing? I recall threads here a long time ago talking about aircraft that had vehicles, tractors, piles of sand etc put in front of an aircraft because of non- payment of landing / parking charges. I would doubt that action could be interpreted as endangering an aircraft.