Just because it can corrupt anyone does not mean it will; the thing is that anyone who is not careful and allows themselves to dabble with evil or does not take it seriously (scoffing at warnings, ignoring clear signals, etc.) can find themselves falling into what they thought they were "too good for".
But some do heed the warnings and take it seriously. Luke is an example in this case: he was headstrong and a bit cocky like his father, but unlike him, he took the danger seriously enough in time to escape it (albeit not without cost). He realized the path he was about to take and rather than follow his father, let himself fall to what he thought would be his death. It did turn out that he would live, but he decided that Vader's way was not compelling enough to follow.
You don't need to know someone's past to know their character; you simply need to watch what they do over time, and see who they are as they make choices and treat others. We do this everyday with people we meet, become friends will, even fall in love with. Eventually we may find out about their lives, but we don't need an entire biography to see their character
Lastly: our character defines how we will react in any given situation, Dark Side or "disaster movie". And events like disasters leave their marks on people in very tangible ways, both physical as well as emotional. We can end up changing and even becoming a different person due to events, seeing things through "a different lens" than we used when we started. I prefer to see Anakin in that light; a good Jedi who ventured a little too close to the Dark Side, events went sideways and he was seduced slowly, whittling away at his defenses and lulling him into a false sense of "being in control", until it overtook him and snuffed out the rich, vibrant man he once was.
THAT is more of a tragedy in my book; the trainwreck that others around him would have watched slowly happening, yet did not/ could not stop.
