I feel like people are getting mad at the FBI for not pulling the trolley car lever in the right way, which is a valid thing to be mad about, but I believe the FBI made the right choice.

First, let's not rely too heavily the analogies with drugs or prostitution. The differences between CP and drugs / prostitution are too large to ignore anyway.

CP consumers are often producers as well. That's a fact—you want CP, so you make some yourself and swap it with others to get more. This isn't universal but it's common enough that you should know about it. So the visitors to the CP web site are not all just consumers of CP but many of them are producers as well. This is relevant because you have to weigh the damage of distributing CP against the benefit of catching people who produce CP. People have stated that distribution revictimizes the children, but I would weigh that against the ability to catch people who were either producing their own or at least supporting other producers of CP.

So the FBI discovers this server, operates it for less than 30 days with a Tor exploit, and catches 200 people using the site. Yes, the FBI was complicit in the distribution of CP, but rephrased as a trolley car problem, this is basically like not pulling the lever, allowing the distribution to continue for a short time, and using that to catch 200 consumers—and how many of them are producers? You can pull the lever now and stop the distribution of CP, or you can let the trolley barrel down the tracks for a short time and save all these people somewhere else.

(People are saying that the exploit may have done damage to other police investigations from other countries—I don't see any evidence that the exploit damaged the computer, merely that it leaked information about the computer.)