Some good points highlighted in this thread regarding a response. Here a a few quotes that may be useful too:
Could a Christian celebrate 25 December as the conception of Jesus? Notice Russel's view on the matter:
"...we could not be certain that the exact day might not be in September about the 27th, but October 1st, B.C. is about correct. Nine months back of that date would bring us to about Christmas time, 3 B.C., as the date at which our Lord laid aside the glory which he had with the Father before the world was made and the taking of or changing to human nature began. It seems probable that this was the origin of the celebration of December 25th as Christmas Day. Some writers on Church history claim, even, that Christmas Day was originally celebrated as the date of the annunciation by Gabriel to the virgin Mary." (The Time is at Hand, Vol. 2 of The Studies in the Scriptures, p61)
Does it matter that December 25 is not the birth date of Jesus? Note the reasonableness that Russell displayed:
"Christmas Day, in celebration of our dear Redeemer's birth, has for centuries been celebrated on Dec. 25; and although it is now well known that this date is in error...nevertheless, since the Lord has given no instructions whatever upon this subject, and since it is proper to do good deeds and think good thoughts upon any day, it cannot be improper, ...for us to remember in a social way our dear Redeemer's birth at this time."(Zion's WT, Dec. 15, 1898-pg.370)
"..we may properly enough join with all whose hearts are in the attitude of love and appreciation toward God and toward the Saviour." (Zion's WT, Dec 15, 1903)"Even though Christmas is not the real anniversary of our Lord's birth, but more properly the annunciation day or the date of his human begetting (Luke 1:28), nevertheless, since the celebration of our Lord's birth is not a matter of divine appointment or injunction, but merely a tribute of respect to him, it is not necessary for us to quibble particularly about the date. We may as well join with the civilized world in celebrating the grand event on the day which the majority celebrate - "Christmas day."" Zion's Watch Tower 1904 December 1 p.364 "It matters not particularly that Dec. 25 is not the anniversary of our Lord's birth, according to the Scriptural account; that really He was born about September 25, nine months later. One day, as well as another, will serve us to commemorate our Savior's birth in the flesh, as a gift of God's love to a condemned and dying world."(Zion's WT, Dec. 15, 1908-pg.379).
So the point is not about "ancient pagan festivals", or that it was not the actual birth date of Jesus but when the Scriptures are silent on a matter, then it should be left up to an individual's conscience to decide - something the WTS denies its membership