As a player, these are two of my favourite gods. Mainly because I usually play as an evil character, and in my opinion these two Daedra are the most sinister. It makes sense that I would do favours for these guys as I enjoy the feeling of being evil in a fantasy world. However, we all know that cults such as the Mythic Dawn have existed. While they were promised special rewards for helping Mehrunes Dagon invade Tamriel, I highly doubt that he would stay true to his word. I'd like to see if anyone disagrees with me, but I can't help seeing a similarity to Satan in that regard.
Now onto Molag Bal. This makes less sense to me. King of [censored], slavery.. Harvester of souls. Does this sound like a fellow who appreciates a favour? Yet there are those who assisted him in his attempt to merge Coldharbour with Tamriel.
I want to know how a citizen of Tamriel would come to worship these two Daedra. Unlike Boethia, or Mephala they have not benefited Tamriel in any way shape or form. Who could be so blind as to worship these gods who clearly offer nothing in return for their worshipers deeds. If anything, all it does is ensure you a horrific afterlife in the Deadlands/Coldharbour.
Thoughts? I am by no means a lore master, but this subject intrigues me.