I don't believe its the Mass they hate although they may say so to get a rise out of their audience. There are defense mechanisms involved here and I'm not sure which ones (displacement & rationalization?). It's not the Mass; it's what the Mass represents to these people. It represents an authority that is not their own (Rome), chain of command, Canon law, etc. Plus it represents a threat to the pervasive "pastoral flexibility" which dominates Amchurch.
The same principle applies to the One Dimensional Christians who ridicule the Mother of God and the Eucharist. Mary and the Body of Christ represent (to them), the Catholic Church and the challenge/threat it presents to their own autonomous authority and freedom to do whatever they wish without any higher earthly authority telling them different. The heresy of 'individual interpretation' permits it, you see.
Knowing that there is a large group of apostolic Christians who will prove to you that you are WRONG using the bible itself to do so, is a threat to the ego. Defense mechanisms are the means of coping.