I think locking vehicles is fine, in many situations:

   1. Capital ships and AT-ATs (which are ground-based capital ships, really) and anything similar shouldn't be usable by the other team. The only exception should be if it's part of the objective of that particular map.

   2. In certain maps such as our current space maps, or lagueriniere's Rakata_Prime - if the map's design is such that it's going to be difficult to get to the enemy fighters and get inside, they may as well be locked.

Otherwise, however... the Battlefield series is all about not leaving your vehicles available for the enemy to take. The Star Wars universe is all about using vehicles with which you're not familiar.  Now, some of these film examples use Jedi, but no one's ever said that "good pilot"="jedi power".

   1. Before the Battle of Yavin, Luke had never flown an X-wing. Yes, the controls were similar to his skyhopper back home, but flying in space would be significantly different.

   2. Lil' Anakin flew the Naboo fighter - his first flight (not hover) vehicle piloting against the Trade Feder... ah, forget that one. I don't like thinking about Ep. 1.

   3. And my favourite example: Ewoks started driving an AT-ST. Granted, Chewbacca took over, but they did start the thing walking. 

Add to these sorts of things happening in the SW universe the fact that many of the Rebels were defectors from the Empire, and you've no doubt got training which would include using enemy equipment. When they had time for training, that is. And much of the Rebel equipment was stolen Imperial stuff, too...

Really, the main reason I posted all that 'slicer class' stuff was a way to compromise between the two viewpoints.  I like stealing enemy vehicles. Taking an enemy AT-ST is fun! That bottom-dropping out of your stomach feeling when you realize an enemy is in one of your side's vehicles is second only to the feeling that you get when you realize you're giving the enemy that same feeling.  

Conversely, while it might give a Rebel that feeling of desperation to see your AT-AT coming toward him, and it gives a similar feeling to you to see the AT-AT stolen and turn on you... The fun level drops off quickly if it happens. The map balance is suddenly screwed up.  The level of confusion/fear/excitement having a rebel AT-ST attacking the Imperial control point is intense, and fun. The much higher level of excitement gives way to disappointment When it's an AT-AT, or a Lancer.