Of course, a downside is a person can set out to invent something entirely on their own, succeed in doing so, and then find out what they've done is illegal. That's a big downside.
Paul Graham said if you're successful you will be sued by patent owners. How many are discouraged from even trying?
This is where experience comes in, and the need for good mentors. In many cases, you can explicitly define your solution with certain key differences relative to prior work.
That is why it is wise to have good patent lawyers on your team. You may still get sued, but your likelihood to prevail can be increased.
Companies know this, that is why it is often cheaper for, say, Apple to purchase entire start ups than to sue them. The inventor still benefits in this case (actually, they can benefit more than typical inventors when this happens).
Paul Graham said if you're successful you will be sued by patent owners. How many are discouraged from even trying?