I don't mean to start shit again, but isn't the reason why vampires have a zero tolerance policy three fold:
A. At varying rates, some quicker or slower, their dark-magic sustained nature drives them (typically dangerously) mad unless they fulfill extremely unlikely categories (dragon blood, Genevieve's very lengthy questline, others I do not know of, etc.)
B. Vampires fall in with other vampires, because sires have direct control over thralls that only fades with, by human reckoning, substantial time.
C. Related to A and B, they eat people.
Ergo, if Mathilde is turned even assuming we're not then executed, or we don't successfully off ourself, we'd be spending decades serving whatever (very powerful) vampire sired us with only some wiggle room, while slowly going insane at a rate dependent on lifestyle and bloodline, and thus will almost certainly not be aiding the sane factions.
Or, so my explosure to Warhammer and reading the entry level official fictions has lead me to believe.
I would say not exactly, I think part of the reasoning for why vampires have zero tolerance policy on them ranges from the factions, for the Empire mainly because major factions of vampires keep on trying to conquer it, for the Druchi mainly because they do not like them because who made them in the first place, the Dawi because of again major factions continuously pissing them off as noted by Boney and the elves from what I can find it is because of the magic being loathsame either because of its design or because of it deriving from the Druchi.
"Only men, with their short lives and shorter vision, could have imagined such a loathsome use for magic." —Ithilweil, Elf enchantress
As for the rest of the points,
For point A, not precisely, so long as they feed on Sekhem of other beings according to the Liber Necris, they do not degenerate mentally from their nature except off course the influence of the the thirst on their mind, the gradual movement of time and the outside factors of the world. Along with the fact it is warned that they should not feed on dhar as it has numerous dangers if they saturate in it for too long.
For point B, from what I can find on the Night"s Dark Masters and the Liber Necris, there is no mentioning whatsoever of Sires having direct control over who they Sire but more they are responsible for managing the vampire with the sins of the sired being consider the sins of the sire by other vampires unless there is some source beyond them which supports it.
Essentially speaking, if Mathilde is ever turned, there is nothing which the vampire can do to make her listen and obey them along with that insanity is only guaranteed you follow the Necrach method of feeding while for the other bloodlines, it is not, In actually going insane from the hunger or dhar feeding is considered to be a failure state in the Liber Necris.
From my understanding of the material at least.
I'm pretty sure the curses on the Vampires are the result of pissing off Nagash (by running from battle IIRC). Initially, the flawed Elixir of Life Nefi made only produced the bloodthirst (and possibly gave Nagash a magical backdoor to their soul).
Pretty much, there is a reason why it is called the Curse of Nagash.