They are monetizing the scamming of so many people.
I would have no problem with a decentralized exchange were people can list, buy and sell any token.
At that point, it is a free market and people are solely responsible for the discovery and research process.
What Coinbase is doing is enabling all these scams to ride on the reputation of Bitcoin and Ethereum (which does have a reputation regardless of my opinion about it) and giving them a patina of credibility by actively promoting them in their website.
That is the essence of my beef with Coinbase. I think I now need to expand this into a full article :)