I’ve always disagreed with that statement.
The enemy of my enemy is …. My enemy.
Case in point. The Nazi/Azov forces in Ukraine vs. the para communist forces from Russia.
When one hires or recruits Mercenaries, does the Mercenary’s religious or moral convictions matter?
Ukraine needs to succeed as their very survival depend on the outcome.
From solely a military stand point, if a Battalion of 1,000 men are willing to help you achieve victory and they’re eager to kill your enemy, in this situation it would be foolish to reject the assistance.