Different people find enjoyment in different parts of this game. It's not like a single player game where there is a straight storyline and then you win. While FFXI has storylines, and some people find it very enjoyable to get Rank 10 in all three cities; others couldn't care less. Some people want to get several jobs to 75 with full relic/god gear/whatever in the shortest time possible. Some people like fishing or crafting or helping out lower level players with quests and missions. Some people just want to chat on their LS or in /tell with their friends.
Like it or not, some people buy gil to avoid a part of the game they don't like, to reach a goal they want.
FFXI is a game constrained by limits. Limits in the amount of exp/hour, limits in drop rates on "good" gear, limits on how often mobs pop.
Each of us as individual players finds parts of the game that they enjoy and fits that around the limits imposed by the developers as best they can.
I have an LS-mate who wants a Brown Belt. He has so far been unable to get the drop from Morlborger. I'm sure he could earn the 3 million or whatever a Brown Belt costs but to him completing the quest is the important part. So he does without and continues to try every once in a while against the mass of people camping.
Some of those campers are no doubt botting/hacking, another "cheat" just like buying gil, that allows the user to circumvent the limits of the game. I am sure that some of those botters are gil sellers; and some are just players looking to make some easy gil to buy some other piece of limited gear that will help make their personal FFXI experience more enjoyable.
Making moral judgements that always assume our personal way of playing the game is superior to all others is just wrong.
As for the golf analogy, why should I care if another golfer has more expensive clubs than I? I'm out there for the exercise and fresh air and some time at the 19th hole with my buddies. Maybe someone else is out their to be the "hole in one" champ and a third person is shmoozing business clients and a fourth is using his compressed air gun to show off his marksmanship skills. None of this matters; what matters is when there is only one golf ball and all four of us want it; and there won't be another golf ball for 21-24 hours. Now we have a conflict. I'm more deserving because I'm playing the game for the pure enjoyment, the Hole in One champ is more deserving (in his mind) because of his elite skills within the rules of the game, the air gun guy thinks he is more deserving because of his creativity in circumventing the rules of the game; and the rich businessman... well, we all know how rich businessmen think.