What it does come down to is. "Do you beleive God is the supreme creator? Do you beleive he meant it when he said to not learn the ways of the pagans"?
I assume from your argument, then, that you don't wear a wedding ring, celebrate wedding anniversaries, or send flowers to funerals? I further assume that you don't use the common names we associate with the days of the week or the months of the year? Because all of those things have pagan origins, and, according to your reasoning, would be offensive to God.
I do believe that God said at Deuteronomy 18:9 not to learn the detestable ways of the pagans (and I notice that you left out that important word in citing the text). Not everything that has ever been associated with paganism in any way is automatically detestable to God. Further, the command was given to Israel as part of their national law, and therefore may not be normative for Christians at all (as the commands to avoid eating pork and shellfish, to keep the Jewish feasts, and to sacrifice animals are not normative for Christians). The key to determining whether such a command to Israel is also binding upon Christians is to find out what the New Testament says on the subject.And what does the New Testament say about celebrating holidays? Check Romans 14:4-8:
"Who are you to judge the servant of another? To his own master he stands or falls; and he will stand, for the Lord is able to make him stand. One person regards one day above another, another regards every day alike. Each person must be fully convinced in his own mind. He who observes the day, observes it for the Lord, and he who eats, does so for the Lord, for he gives thanks to God; and he who eats not, for the Lord he does not eat, and gives thanks to God. For not one of us lives for himself, and not one dies for himself; for if we live, we live for the Lord, or if we die, we die for the Lord; therefore whether we live or die, we are the Lord's."
There is no command to Christians to avoid celebrating any holiday that at one time may have had pagan associations (if it even did - one argument in favor of Christmas is that it was established in opposition to pagan feasts, not as an acceptance of them). To try to build such an argument based on a command from the Mosaic Law flies in the face of Christian freedom, as expressed by Paul in Romans 14. If we "observe the day for the Lord," in a Christian manner, as a celebration honoring Jesus Christ and commemorating His birth, there can be no scriptural objection. If, on the other hand, you feel that whatever pagan associations the holiday may have had in the past make it objectionable, it would be wrong for you to celebrate it - however, it would be just as wrong for you to attempt to make a blanket rule for those whose consciences differ from yours.