One way of determining if people are good, or more pure-hearted, or bad is through their actions.
Bad things Fred and George did:
-Teasing their family and friends in ways that wasn't even teasing or funny, it was just cruel. I know siblings tease each other, but that doesn't make it okay.
-The Big One: they "used the family Puffeskin for Bludger practice." As Beaters, that means they hit the animal with heavy bats. It is unknown at what age they did this, but likely once they were already Beaters, so at least 12, way past the excusable age.
-Turned Ron's teddy bear into a spider, causing his fear of spiders. Considering he was more afraid of spiders than, you know, the lunatic trying to kill him and his best friend, I'd say he was traumatized pretty thoroughly by that.
-Burnt a hole through Ron's tongue with an Acid Pop.
-The Second Biggest One: Almost killed Ron by trying to get him to make an Unbreakable Vow.
-Stole from Filch's office, not even knowing what the Map was.
-Reorganized library shelves, just to waste the librarian's time, if you consider Hogwarts Mystery canon.
-When reorganizing library shelves, made George take the blame for Fred's actions.
-Also from HM, insulted Sir Cadogan and Merlin's paintings.
-Teased Ginny when she was very emotional fragile from the diary. They may not have known about it, but it's never okay to "tease" someone like that.
-The Third Biggest One: Tried to push Percy into a pyramid.
-Insulted Scabbers when Ron was upset about losing him.
-Fred wanted to blackmail Ludo Bagman
-Tested their prototype products, which were designed to cause discomfort and pain, on first-years, and others in general.
-Shoved someone who was basically innocent into a Vanishing Cabinet
-Sold love potions, which is so wrong on so many levels, I can't even talk about all those reasons here, so I'll leave it up to your imagination.
-Sold products designed to harm people in their shop
Good things Fred and George did:
-Joined the Circle of Khanna, if you consider Hogwarts Mystery canon.
-Joined Dumbledore's Army to fight against Umbridge's oppression
-Rescued Harry from being locked up
-Defended Harry in the Battle of the Seven Potters
-Defended Hogwarts students in the Battle of Hogwarts
-Helped with Potterwatch to spread the truth
17 bad actions and 6 good actions... not looking good for these "good" guys.
But what about the motive for all those bad things? Surely that could explain it... oh wait, that's right, their motive was to entertain themselves. Oh, that's so much worse.
I don't think anyone could argue that they were good people, or even neutral people, but you can try.
This is a debate post, keep in mind.