I think the key word in the poll question is "instead". There is nothing wrong with "Happy Holidays" by itself, but when it is used to the exclusion of "Merry Christmas" it is offensive.
I am not really offended by it even if it is used in place of Merry Christmas. What I take offence to is the tone of the people who say it purposely to denigrate Christmas
Example, Stinkhole Madonna(the slut singer) has a greeting running here in Germany and you can hear it in her voice that she is saying Happy Holidays with the purpose denigrating Christmas.
Maybe I am hearing it wrong or I just despise her that much but it is playing here and it is offensive to me. But hey I am the visitor here. I don't know Madonna's views but I can only guess what they are.