I have a general feeling that they're bad (the org, not the individual children lmao) but am fuzzy on the details of why. It's generally agreed among leftists that it's child labor right? And that they love teaching little kids that capitalism = cool and good. I've got a niece in girl scouts and I'd just like some more concrete examples and reasons not to support them so that my family understands that I'm not just being cheap... although yeah ok I admit it the shrinkflation over the years is one of the reasons I don't give them money, fine.
Or uuuuuh if you think they're good actually then explain for the class pls. Make me feel bad about buying knockoff treats for a third of the price and then not donating the difference. 
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If you can find alternatives that don't feed into the whitewashing of the genocide of indigenous Americans I'd go with that. It's fine for kids to have a nice org that is nice to them (scope it out to verify that first) and has them do outdoor activities so I'm not saying to just write them off entirely but it's something to think about.
In my neck of the woods there are independent orgs that still do camping and outdoor skills and art and so on but actively incorporate indigenous Americans and cultural practices and history into it and I think that's a much better way to go. As a contrast, scouting tends to feed into the path where being an "outdoorsman" means replicating the white settler experience, or at least a mythologized version of it.
Damn I didn't even think about it from that angle!
Order of the arrow can be particularly egregious on that front