The European Fatwa Council; made up of 20 of the worlds greatest Muslim Jurists, stated that it is permissible to greet people on these days (exchange gifts even) as long as it does not involve approving any creedal differences between us, or open evil (drinking and so on). In other words, a simple happy holidays is not a sin or going to take that person out of Islam. It is reported with authentic chains that Ali (ra) celebrated the Persian New Year, even eating ice cream with Imam Abu Hanifa's relative. Many of the fatwa quoted by sincere folks are rooted in an age of empire and war (the crusades) or a social reality that does not fit ours in the West. Most importantly, a person should ask those who use words like "haram" "kufur" "Halal" and "encouraged" about their religious training. Yelling and over blown emotionalism does not equal training and scholarship. Allah knows best
This person thinks he is better than Ibn Al Qayyim:
Ibn al-Qayyim, may Allaah have mercy on him, said in Ahkaam Ahl ath-Thimmah: 'Congratulating the Kuffaar on the rituals that belong only to them is Haraam by consensus, as is congratulating them on their festivals and fasts by saying ‘A happy festival to you’ or ‘May you enjoy your festival,’ and so on. If the one who says this has been saved from Kufr, it is still forbidden. It is like congratulating someone for prostrating to the cross, or even worse than that. It is as great a sin as congratulating someone for drinking wine, or murdering someone, or having illicit sexual relations, and so on. Many of those who have no respect for their religion fall into this error; they do not realize the offensiveness of their actions. Whoever congratulates a person for his disobedience or bid’ah or Kufr exposes himself to the wrath and anger of Allaah'.