The real question is not "did they make the right decision" it's "do we care?"
Marty is no prize. The girls are no prize. And BOTH Suzanne and Stacy were incredibly annoying in very different, but complete ways.
As for whether or not what they did to Suzanne was right? It probably wasn't. It was likely very evil and despicable. But that fact is not enough to suddenly shift all of my impressions of these people into building some magic fantasy where Marty and Suzanne are lovely nice people who I care about, who deserve some fairy tale together, and whatnot. I'm setting these things apart in my mind, personally.