Those groups are representing people, and yes, in an ideal world, in which politicians simply represent their constituents, they would be unnecessary. In a democracy, public policy is supposed to reflect public opinion. Yet, there is endless political science research showing that public policy usually has very little to do with public opinion. That is because under capitalism, capital concentrates, and it then uses that concentrated capital to influence public policy through legalized corruption (lobbying). If whatever some megacorp is lobbying for were actually in the public interest, and public policy reflected public opinion, there would be no need for their lobbying. They lobby because their interests are not aligned with the public’s interest.

There’s also no union for “the public” which is a little unfortunate since that should basically just be the government.

So yes, TLDR, first restore democracy and then we can talk about whether we need unions anymore. Until that time however, they are the only mechanism the public has to try to wield some degree of influence comparable to that of capital.

In other words, yes, big oil lobbying bad and auto workers union good.