A lot times, though not all, when people do something they feel it is particularly righteous, it is a very shortsighted approach that lacks a more holistic consideration of other variables. Is there a name for this tendency of where the more right someone thinks they are, the more damage they end up causing? It's almost like a kind of high-risk high-reward situation.
I still believe this Q&A belongs on English Language & Usage, but since it hasn't been deleted yet, no sense in letting the question going on unanswered. So...
Like Guy Inchabald, I'm not familiar with a single word in English that meets your specifications, however, there are some related phrases. First, consider the phrase 'The road to hell is paved with good intentions'. It's a well-established idea among peddlers of saws and adages that more than not bad actions are because of ignorant people. Sometimes it is expressed as 'There are no bad people, only good people with bad ideas.' It also has attained the status of philosophical razor in the form of Hanlon's Razor where one is entreated to consider that it is more likely bad outcomes are a result of ignorance rather than malice.
If we were to attempt to use a phrase in a context, one could just use the adjective 'well-intentioned', 'incompetent', or 'ham-handed'. So, let's take a number of terms such as do-gooder and use adjectival modifiers:
The important thing is that we find two words that carry a contemptuous connotation while encapsulating both denotative elements of 'failure, badness, incompetence' and 'well-intentioned, trying to achieve goodness, etc.'.
A villain who has an overall goal which the heroes can appreciate in principle, but whose methods of pursuing said goal (such as mass murder) are problematic; despite any sympathy they may have with their cause, the heroes have no choice but to stop them. Taken to extremes, they may fully believe that Utopia Justifies the Means. Such an idealistic extremist is likely to be either a Totalitarian Utilitarian or a Principles Zealot, depending on whether they’re aiming For Happiness or For Great Justice. The most well-written examples of this trope are the kind that the reader/viewer stops just short of agreeing with.
This is related to the psychological term 'true believer' which is used to describe a person who has generally is involved in a mass movement or other political ideology who acts in accordance with a representation of the world that tends to be highly resistant to empirical evidence.