It's an example of something that's being ruined by misuse, even though some people have good intentions. Mercing is a problem because it lets people get the rewards without doing the work. You might say it's fine to pay gil to skip content, but in many cases it also means paying real money to skip content.
This also has a secondary problem of people not learning from their experiences when they do this, causing people to be geared for content but without really knowing how to use the gear or play the game well.
