Technically, you can trade. F2Ps can trade tools received in drop and items received in trade. If you play enough to drop a bunch of tools, get people to give you items for free or in exchange for other things than TF2 items (insert innuendo of choice) and then trade consciously, you can slowly but surely make a profit.
~ Signed, F2P player with cosmetics for every class and a 150-slot backpack.
Spending a dollar in the store is a lot quicker and easier, though.
Ah, and to answer your question: TF2 is a great game and well worth paying for, and the way it executes it's free-to-play-ness - With all maps and everything that impacts gameplay (except polycount sets but whatever) readily available for free without any time limits - is incredibly generous. Stop complaining.