Consider that slasher films, for the most part, come out of Reagan-era conservatism, and feature a male killer killing a number of young women, often educated and having fun (classic older male resentment). Consider that 99% of violent crimes against women are committed by men.
High Tension could well be read as a film about women's rage against patriarchy being played out in a peculiarly self-destructive way.
I agree that it's possibly very misogynistic, but it's a lot more complex than, say Halloween, or Nightmare, or Friday the 13th, which are essentially meant for idiots.
it takes women twice as long to die as men in these films. Females are shown in terror for obviously longer periods of time than males.