Because empirically it would not be. There is a great deal of mis-information about them from right leaning media that might create the contrary impression:

That they limit wages, but the screen actor's guild certainly doesn't cap actor's wages.

That they limit outside work, but for example, state employed court reporters do all their transcripts outside working hours and make quite a bit not being paid hourly for that.

Indeed they have protected pilot wages for decades beyond what would have been possible otherwise.

There is no case where an effective professional organization of some sort doesn't make things better for it members. To suppose that you as an individual will ever have any hope of negotiating on an equal basis with a multibillion dollar company because of "market forces" hand waving is utterly unreasonable and the poster child of limiting yourself due to ideology. Your one and only protection right now are few pieces of rapidly diminishing legislation.

For better or worse you live in a society where if you don't have a lobbyist you are invisible and where what is considered bribery in every other country (ie money in politics) is considered free speech. A lobbyist alone would work wonders let alone the other advantages of an organization.