When the blind lead the blind, they both fall into a pit, as Jesus Christ famously put it. And the gravity of the blind leaders' wrongdoing would be lessened were they merely blind, but their claim to be able to see means that gravity remains.
What is a mercenary? The answer given to this question might be a matter of life and death for those who fight in the wars of foreign countries. To try to circumvent this, there are groups such as the French Foreign Legion which tries to give non-mercenary status to its foreign fighters. Ukraine did something similar in a hurry this year. It set up its own International Legion of Territorial Defence of Ukraine. In an announcement of this, the Ukrainian Foreign Minister Dmytro Kuleba gave the game away by mentioning that some of the home countries of members of this legion forbid their citizens from fighting for other countries. [1] Even the UK has such a law, although it is rarely applied. It does not take much common sense to work out that if a country forbids its citizens from fighting in wars against countries against which the UK is not at war, then the reason for this is to do with the common understanding that such fighting is considered mercenary fighting, and is therefore not given Geneva Convention protection. The UK in recent years seems to have sought to play down the distinction between a mercenary and someone fighting in such an international legion. Unfortunately this muddying of the water may have helped to persuade British fighters to embark on actions leading to their deaths. Ref 1[1]: https://www.timesofisrael.com/liveblog_entry/ukraine-says-20000-volunteers-from-52-countries-sign-up-to-fight
