Let's put it this way: You are a squad leader. You spawn on the hovercraft. You jump off. You don't immediately open your parachute because you're not an idiot. You skydive down close to the ground and then open your parachute. Your squad spawns on you, maybe one of them places a beacon, maybe not. You attack the point. Your squad fails to take the point but you have pinned down a portion of the enemy team trying to wipe you out.I've never seen anyone complain that the hovercraft gives one side an "unfair advantage". Choosing a spawnpoint that allows you to easily get shot out of the air while and takes significantly longer to get to point compared to other points isn't advantageous. If anything, the side with the hovercraft is at a disadvantage. Whenever my team had a flying hovercraft, the only time I would spawn on it was if I specifically did not want to play that map and wanted to take the extra time to drop in. Maybe for bz admins there's "no argument", but I genuinely have not seen a single person who actually plays on the server that was supposedly affected who voiced a problem with flying hovercrafts.
Up until now you're still in the realm of normal gameplay. Afterwards here is where it starts to become unfair. You keep spawning on that hovercraft. You keep doing the same thing over and over again. Eventually more and more of their team starts defending the point you're attacking. They start to suspect you have a beacon hidden somewhere. They begin to look for it. Their search however will be fruitless since there is no beacon, or if you placed one it is destroyed but you still are able to spawn there because of the hovercraft. Nothing the enemy team does can in any way dislodge you from contesting the point because you still have the hovercraft up in the air acting as an invincible beacon. The problem can become even worse if the guy doing the hovercraft glitch starts to yell to his team in chat "Spawn on my hovercraft, we can take Bravo with it!" While this kind of communication is normally a good thing in this case it is abusing something that the enemy can do nothing about.
Maybe your squad's actions turn the tide of the game and win you the match. Maybe your team is so dogshit that even with your exploitation of the hovercraft you still lose. Maybe your team was dominating the other team anyway that your actions had minimal effect. Whatever the outcome turns out to be the fact remains that you benefited from the actions of a person who abused an unintended effect in the game for which there is no reasonable way to counter it. This last part is the most important : there is no reasonable way to counter it. Many glitches exist in the game which can provide an advantage. Third floor on Metro and voozooing and other movement glitches are just two examples. The difference between those glitches and the hovercraft one is that the hovercraft one can not be countered. Similarly glitching into the mountain or ceiling on Operation Locker is also prohibited because it too can not be countered.
Can you see now how this glitch can affect a game? How it is able to provide a demonstrably unfair advantage - even if it is a small one - to one side over the other?
Maybe banzore's zero-tolerance policy is too much. Perhaps a person can commit this offense in good faith without any ill intentions. Perhaps they even can have committed it without knowing that it was prohibited. But at what point is the line to be drawn? The first offense? Second? Third? The offense which only resulted in a material advantage to the team? What about the offenses which don't result in an advantage? Being inconsistent in an application of your rules is going to create even more headaches and frustration for the players involved. Players will not know what actions they can perform and what actions they can not. Every single second on the server will be wrapped in fear and anxiety that something, somewhere someone does will result in their being banned. This is hardly a way to maintain a population on a server in an already-declining game. In this case the admins have decided to draw the line at the first offense. If you wish to disagree with that then that's fine but failing to understand why the rule exists as well as how it is applied is willfully ignoring the reality of the situation simply because you disagree with the outcome.