I agree with getting vocal .. but don't boycott
Go to the parade and sing Christmas carols
Spend your money elsewhere. The economy won't tank, the corporations will take notice.
The event planners will take notice when they only draw 10% and few children.
The left doesn't care "why" people go, so long as you are there. The more people they can claim "went" the more they can claim in the media and to superiors that their event was a "success".
Meanwhile, we can celebrate Christmas every day (Easter too!). Any time you want to take the opportunity to remember Jesus' birth or resurrection, you can. Try saying "Merry Christmas" to every stranger you meet, especially retailer. Every day. All year.