But GDAX is a vertically integrated exchange and retail trading platform, so the 0.1% taker fee is all you pay. A stock exchange won't talk to you directly so you must pay additional broker/clearing/bank fees.
Real all-in fees for stock can be 2 USD to trade 2k USD, so 0.1%, same as GDAX. But you can also find fees of 10 USD to trade 100k USD and many other rate examples which are either higher or lower.
I think a lot of people don't notice the huge difference between a traditional exchange (which does not handle money, only agreements about money) and GDAX (vertically integrated exchange + clearing house + trading application).
I'm perfectly fine paying 10 cents for every $100 I trade.