The world, and history, has always been a struggle between groups with competing and conflicting intersts. Good and evil exist, of course, but it is never a province of one side or the other in any conflict. Both just arise as part of this tapestry of struggle. They are both the result, not the cause, of conflict.
Ideology arises as an attempt to distract us from this endless and inevitable struggle with an artificial world of good vs bad, us vs them, left vs right. It seeks to replace an understanding of why things happen with a simply demonized foe which can be hated, and then eliminated. Unions are not immune to corruption and greed, they are not endowed with a guarantee of virtue, they are simply an organization of a class of people with similar interests in order to counter the interests and organization of the commercial classes they see as their adversary. The same can be said for their opponents.
The danger is not so much that one side will take over, it is that one side will will confuse natural and wholesome competing interests with a moral struggle. Beware of principles and morality, they do exist in nature, but absolutes do not, and those who proclaim them the loudest are usually those with most to gain by ignoring them.