OK, if this isn't a sign telling you "DON'T DO THIS", I don't know what is. If Yuyuko really is under the tree's spell, this is the exact reason she wants to see Youmu in the first place.
Also, none of you seemed to mention what we do AFTER we free Yuyuko, assuming we go with that plan and it succeeds. We'll just have an enraged tree on our hands, with no immediate way of calming it. Hell, I'm predicting Youmu or someone else (aka, Youmu, pretty much) would have to sacrifice herself.
Basically, both of these scenarios will likely end really badly, so unless we have a very good plan, put them on hold. As for the plan, well, I'm not feeling very creative today.