The mace isn't corrupting you (as far as I can tell). It's basically power with no drawbacks (other than being weak compared with other magic items).
In general, I agree that the various daedric artifacts come with too few strings attached. However ...
(1) Generally, the daedric gods gift you with their artifacts because you've already demonstrated your suitability for their purpose.
Case in point, Molag Bal: by the time you've got the full-fledged mace, you've (a) tracked down and freed a minion of M.B.'s rival; (b) deceived or dared said minion into returning to Markarth to resume his desecration of M.B.'s shrine, knowing full well it's a trap; and, (c) beaten a helpless old man to death with a rusty mace.
Twice.You don't get the mace so that it can corrupt you; you get the mace because
you are corrupt.(2) The idea of the daedric princes givin' you their stuff is not so much, seemingly, that they expect you to consistently serve their will (though some certainly act like it-- I'm looking at you, Meridia). It's that
when you use their stuff, you
are working their will. Use the Mace of Molag Bal with a soul gem equipped, and you are first weakening your enemies, then crushing them utterly and stealing their souls. M.B. doesn't give a damn who you beat, so long as you're using the mace to do it ...
... and even if you never do, eventually someone else will acquire it.
Similarly, you are working Azura's will each time you use her star (or thumbing your nose at her and her relatively benevolent intentions each time you use the Black Star to trap a human soul); you are stealing dreams for Namira every time you use the Skull of Corruption to, well, steal dreams; and you are harvesting souls for Mehrunes Dagon each time the Razor insta-kills someone (that's how it works-- slurp! "Your soul is mine").
You are praising Boethia's name (and mocking all notions of honor) by trotting around in the Ebony Mail, spreading chaos for Sheogorath by wielding the Wabbajack, giving one of Sanguine's minions a bloody night out on the town by using the Sanguine Rose, praising Namira with every nibble you take from a corpse using her Ring, enforcing Peryite's order by wielding Spellbreaker, and giving glory to Malacath with every skull Volendrung staves in. The Oghma Infinium vanishes from your hands once used, spreading Hermaeus Mora's Lovecraftian influence elsewhere in the world, while the grant of knowledge it gives remains behind in your mind, a testament to his power. If you use Dawnbreaker for its sole useful purpose at all, you are serving Meridia's will by hunting the undead.
About the only daedra who seems to care at all who you use her artifact on is Mephala, and that's because treachery is needed to strengthen her Ebony Blade. Once you've killed ten of your nearest and dearest, she could care less.
Every daedric prince bestows power on the dragonborn in the hope that
it will be used. That is the only motivation necessary; with the exception of Azura and Meridia, none of them gives a damn who you use that power on. Callous disregard for life is a hallmark of the daedra. I only wish that it were more consistently desirable to use the power they offer (the artifacts should be either more powerful or more consistently unique).
Yes, I'm an enormous TES fan. Yes, I think I'll be giving this one a pass, because it seems like so much of what I love from TES is flatly impossible in an MMO.
I have never played an Elder Scrolls game...
Seriously, Fantasy is without a doubt my least favorite setting.
TES is much more interesting, as a setting, than most fantasy. For one, it virtually bleeds moral ambiguity. The same person who saves the world is very often, in many, many ways, a Very Bad Person.
As per Morrowind (by way of the Bloodmoon expansion), imagine the second coming of the Messiah as ... um. A werewolf. Who eats people on a nightly basis.
That said, if you can't stand the sight of swords, fireballs, and pointy ears, best steer clear.