The recitation of Yizkor on the holidays presents somewhat of an issue. Within the realm of Halacha, the emotions of Simchat Yom Tov, the joy of the holidays, are deemed to be inherently in opposition to those of Aveilut, mourning for those who have passed away. They're potential co-existence is, thus, always a halachic issue with the former, generally, overriding the latter. Is the recitation of Yizkor on Yom Tov, thus, not somewhat of a paradox -- why would it be recited on these days?
For further on this, please go to http://www.jewishtribune.ca/religion/2014/06/02/yizkor-there-is-joy-in-the-holidays.
Rabbi Ben Hecht