The whole point is that they are without comparison. There is no other force like it in the world. By definition it may have to be that way (if it should exist, which I'm not entirely sure it should), but so long as there are UN peacekeepers there will be armed troops where nobody's really both motivated and able to prosecute their war crimes with any reliability.
The legal framework surrounding UN peacekeeping is insufficient as the UN itself grants its peacekeepers blanket immunity, and expects host and/or contributing nations to prosecute war crimes committed by UN peacekeepers. But those nations are almost by definition unable to maintain the rule of law (or in the case of contributing nations, unlikely or unwilling to prosecute).
I'm not sure why "but other people also do bad stuff" is where everyone seems to go with that information. But to go along it, a more apt comparison would be the Mahmudiyah rape and killings: war crimes committed by US troops in Iraq, in which the perpetrators were tried, convicted and sentenced in American military and civilian courts. That's how that aspect of the inevitable evils of war should be handled:
https://en.wikipedia.org/wiki/Mahmudiyah_rape_and_killings
Had the perpetrators been UN peacekeepers, the host nation likely would not have had the ability to prosecute the accused competently and fairly, and the UN would have given them immunity if expected to act. The contributing nation would not have wanted to prosecute for a whole host of reasons.
One can argue that the UN is doing what it can, but it isn't much: Asking contributing nations to prosecute war crimes committed by their citizens (not likely), shaming those nations [1], and trying to support the victims [2]. Which all goes to show that the UN is rather toothless on the matter. There's an asymmetry to their ability to contribute to violence but not prosecute the criminal abuses thereof. I think that's concerning.
Regardless, your comparison reminds me that even Abu Ghraib resulted in numerous prison terms. Make of that what you will.
[1] https://news.un.org/en/story/2016/01/521142
[2] https://conduct.unmissions.org/remedial-trust-fund