On Season 10, when Nnoitra thinks back to when he fought Nel last time (when he broke her mask), he got her to fight by hurting Pesche and Dondochakka. Seeing them, Nel said that Nnoitra had ripped off their masks. However, Pesche and Dondochakka are Fracción and thus Arrancar, so their masks have already been removed.
Can Arrancar not fully removed their masks? If not, then how is Nnoitra ripping off Pesche's and Dondochakka's so bad that it was enough to bait Nel into a fight?
In Bleach, when a Whole becomes a Hollow their heart leaves their chest (forming a hole) and transforms into their mask. (Chapter 433)
The powers that a hollow develops and very body arise from the mask.
If the mask is removed, it would logically follow that the Arrancar would lose all of their power. We know that removing the mask from a normal hollow forces them to temporarily revert to their form as a Whole (the Ichigo vs Orihime's brother arc).
While we can't be sure this would happen to an Arrancar, the fact is that stripping an Arrancar's mask would strip away their very identity as an person. It's a horribly cruel thing to do, even for someone like Nnoitora or Syazel Aporro.
