Well righteous (thats how you spell it) is for some cause that you see right in your mind, ruthless is where you do something showing no mercy. sorta a big difference... you can be righteously ruthless, they aren't really opposites...
I mean ruthless are different than the righteous because they show no mercy that's what SkullZero1 said but i think it's that the ruthless are kinda barbaric or i don't know.
Yeah, what Moegreche asked. From a very literal perspective of your question, the 'righteous' keep the rules and up-hold them, while the 'ruthless' will do whatever it takes to get their way.
Well it really depends on the situation. If you are fighting for the "good side," like in Lord of the Rings, then it is right for the "good side," hence the word rightous. Actually, I don't really think those two words are related, haha.
The Mongols were ruthless, but to them, it may have been righteous to invade and help end the Roman and Byzantine empire. I guess it depends on the situation AND the point of view.
There's no real distinction between those who are 'righteous' and those who are 'ruthless' and perhaps even a significant overlap between those who claim that they are 'righteous' and those who have been said to be 'ruthless'.
Despite the invocation of Godwin's law, one could argue that Hitler was both righteous and ruthless. The latter was less arguable than the former but the former was believed by the relevant majority, which then goes back to what 'righteous' actually is.
I believe one of the reasons you raised this question is because of the variety of Biblical interpretations of what 'righteous' is. Sometimes such things are worded very strongly (see some of the Psalms), in fire and brimstone it is made clear that the righteous will prevail while the wicked burn. But then again it is also demonstrated that those who make pains to claim they are righteous aren't really so righteous at all (the Pharisees who constantly antagonised Jesus). And then there is the history of the church as state in the centuries following, and their acts in the name of God and therefore 'righteousness'. How 'righteous' were they then, and how righteous now are certain people in their beliefs and the way they act upon them?
As a guideline I'd suggest that 'acts of righteousness' borne out of hate and differentiation are not righteous.