I will make no claims to being an authority of Druidish history; in fact I had to look 'some' of it up (most of it I knew). In Ireland the Druids, before the Celts arrived from central Europe, built Newgrange in Co. Meath in the years 3,300 BCE. On Dec 21 it marks the end of winter and the start of when the sun shines more each day. SOMETHING REAL- AND WORTH CELEBRATING. They had this figured out more than 5,000 years ago- but yet, in the age of so-called 'high tech knowledge', buffoonish fairy tales still exist.
The winter solstice exists. That's all the acknowledgement it needs. As a matter of fact, it would exist even if nobody paid attention to it. I don't think it makes any more sense to "celebrate" a natural event than it makes to "celebrate" the existence of air.
Well, the Celtic Pagans celebrated it with Yule. Then the Christians came along and tried to convert them by turning Yule into Christmas and the Spring Equinox into Easter. In fact, most of the accoutrements of Christmas, the tree, the lights, the presents are Pagan by background, not Christian. So in a way, we're already celebrating the Solstice each year.
I'm of the opinion that most post modern people (including myself there) are far removed from the cycles of nature. Our ancestors used to be in tune with the changing of the seasons that marked the passing of the year. I have to think hard to remember the last time my bare feet touched the bare Earth, or the last time I sat on the ground beneath a tree. Heck, I don't even mow my own grass anymore. I think a ritual or even just an acknowledgement of the changing cycles of the moon or the changing seasons is a great way to reconnect with the natural world that is all around us.
I do go hiking every now and again or for a relaxing walk on a nature trail, and it's always so calming and balancing for me to reconnect with nature. And I think most of our modern secular holidays coincide with the pagan festivals...we celebrate Christamas (Winter Solstice), Valentine's Day (Imbolc), Easter (Ostara or Spring Equinox), Memorial Day/Earth Day (Beltane), 4th of July (Midsummer, Litha or Summer Solstice), Labor Day (Lughnasadh), Thanksgiving (Mabon or autumnal equinox), Halloween (Samhain).
I try to remember at each of those holidays that it used to mark the passing of the year.