Agents are an issue until they get you the player you want. When an agent unsettles a player that the club doesn’t want to sell then he’s a problem. But when it's time to look for the player's replacement, then the club could use that same agent to unsettle that guy.
Clubs have agents too; they work with them when they want to get to players. Agents are a necessary part of the ecosystem and one of their roles is to be the bad guys. Everyone is working with them - the clubs, the players, the media. They are the powerbrokers and clubs might talk about wanting loyalty but they will put you on the bench or sell you if they deem you not good enough.
The agent is the bogeyman to point at when things don’t go our way. But they are serving a need. Where you stand on agents comes down to what has happened - if you are a fan and you just had a player leave, you probably won’t like his agent. But then your club will work with that agent if they need him to sign a new player.