What can be wrong is someone's selfish interest affecting negatively everyone else. I.e. acting not for the sake of making a useful law for the public, but acting for the sake of making a useful law for someone's particular pocket at the expense of the public. It's very clearly wrong, but how exactly this can be prevented is a good question.
The thorny issue of lobbying vs. democracy shares a lot of overlap with the realities of legal costs and the justice system. On the one hand, it's clearly unjust that the party who can afford more legal fees has a strong advantage, both in and out of the courtroom; on the other hand, it's also unjust to not allow someone to choose their own legal counsel, and how they make their case.
