From experience I know how time consuming and difficult trawling through listings for rooms can be.
Anything that helps narrow down the field is helpful.
That sort of thing is exactly what I need to know. As a married, heterosexual woman, there is no point me applying.
Neither those living in the house or those applying want to waste their time meeting potential flatmates who could be ruled out with a single question.
It's important you get on with your flatmates and have common attitudes and beliefs so it's best to be upfront about who you are and what you are looking for in a flatmate.
You need to be comfortable and able to relax when at home.
We are too concerned with being politically correct these days.
It is logical and useful to include this sort of information in a flatmate wanted ad.
The flatmates who posted the listing have now defended their wording saying, "You are not being discriminated against by us, we just don't want to live with you."
The attitude has to go both ways though. If it is okay to state you do not want a heterosexual flatmate, it has to be okay for others to state they do not want a homosexual flatmate.