This summarize what to me is a major fault with todays big MMOs. You level through questing with small parties and the endgame is raids? You grind your way up against computer AI and then when you are on top you get to PvP?
The problem here is two-fold. On one hand you have the players that are enjoying the leveling content. They get to the level limit and then the game changes into something they might not like. Imagine playing Half-life 2 just to find that he last chapter is an eternal card game.
Then there is the other pack, which are forced to level through content which they are not interested in, in order to play the endgame. If you like PvP, why should you be forced into days upon days of laboring through quests first?
Some measures are usually taken to address these issues, measures which brings to mind words like "band-aid" and "bullet-wound". A system where low level characters can PvP against each other is not a solution. It stops their progression and cuts them off from the actual endgame, ironically enough.
On the same note, if you change quests and small groups into raids at the end game, then you are essentially telling those that actually enjoyed the leveling part of your game to bugger off.
It does not have to be this way. When you start playing a game, you should immediately make meaningful progression in the part of the game that is essential.
Luckily some developers are moving towards this design. Take Warhammer Online as an example. Mythic is using the end game which worked so well for Dark Age of Camelot (Faction vs Faction PvP, or RvR as they like to call it) and removing the horrible grind. They are essentially saying, "Do you want PvP? This is the MMO for you".
While I have not been given a beta account yet, it shows a lot of promise. Everything is designed around the war effort, from the first time you log in and until you are at the top of the food chain, you are involved in PvP. There are quests, and there are NPC objectives, but these are all tied into the war effort. And slowly, as you level, the PvE content is phased out for PvP.
Guildwars is another example of how it should be done. Having a character ready that can compete is a matter of hours, not weeks.
Let us hope that others catch on, and perhaps some time in the not so distant future we can PvP without having to grind our way there through something we do not really enjoy.