Meridia. Regardless of her indifference to the lives of mortals, her hatred of the undead ultimately makes them safer.
What about those who chose undeath in order to protect others?
A perfect example of this is a character from the Bloodmoon expansion: http://www.uesp.net/wiki/Bloodmoon:Draugr_Lord_Aesliip
As you explore about you'll find an area habited by the http://www.uesp.net/wiki/Bloodmoon:Draugr_Lord_Aesliip who will speak to you as you draw near. He will tell you the story of how he was once a mage who became draugr solely so that he could continue to support a barrier that prevents the invasion of Frost Daedra. The barrier has recently become weak and he asks for your help in driving back the daedra invaders.
Meridia would kill this Aesliip without a second thought on the matter.
ALL undead are monsters to her,
ALL undead must be purged for her to be content. However, Aesliip's premature death would be devastating for the mortals who inhabited Solstheim as they would soon all be massacred by the army of atronachs below the lake.
This is one of Skyrim's flaws on the matter, all the undead you meet (excluding a single one from DG) are doing so "for teh evulz", if they even talk about it at all. I have yet to meet one who is doing so for the greater good.
Being undead is not inherently evil or good in TES, even the process of lichdom is pretty neutral towards other people if the mage takes the right approach (it's merely trapping their soul in a temporary container, then moving back to the now-dead body). Though the majority of those portrayed in the games tend to skew opinion negatively on the matter (mainly because of the sheer amount of [censored] that chose it).