WHAT'S SO NEFARIOUS ABOUT LOBBYISTS ANYWAY?

I watch a lot of news, and for years they have been beating the lobbyist drum pretty hard. I know bribing and buying votes is wrong, but I don't think lobbying is (at least as I understand it, which may be criminally naive.). It seems to me like there is a real substantive difference between crooks like Abramoff and most of the lobbyists out there, but all of the pundits and politicians I've heard talk as though they're all the same. They talk endlessly of lobbyists and special interests as though they're all a bunch of sleeze-balls handing out bags of cash so politicians will look the other way on stuff. I know all about Abramoff, and yadda-yadda-yadda, but most of the lobbying seems pretty above board to me, and even important. It seems to me that efforts by special interest groups such as corporations, and industries to influence legislators shouldn't be curtailed so long as their behavior isn't illegal. Why is it bad for groups to scrap and fight for their perspective? It sounds messy, but not unethical. Am I wrong?