I don't think there's anything wrong with being cautious about coming out. I'm in no rush when it comes to my parents. They support me financially but if I told them I was bi, kinky and poly, well, I'm not sure what would happen. Someday when they aren't paying bills for me, (hopefully soon!) I may decide to come out. But I'm in no rush. Some of my friends know stuff. If I feel they are trustworthy. I haven't had too many issues with people freaking out at me. But then again, I've been very choosy as to who I tell.
And asking if America is ready for poly isn't the only question. There seem to be a lot of people in poly relationships that may not actually be ready. I appear to have just been a victim of that. And I know I'm not alone there. I keep hearing stories about couples that try to give a go but really hadn't thought it through or weren't really comfortable. To be fair, I am biased right now.