Why should a woman say "I'm not thinking of getting married !" ?

She doesn't literally have to say "I'm not thinking of getting married" the moment they sit down for a coffee or whatever. Simply, no man is looking on a first date for a potential marriage partner, and he could find it off-putting to find the woman he's dating is constantly dropping hints about the future.

In other words, don't come over all anxious and needy - surely you don't need to be told that?

Can you imagine wanting to date someone and s/he replies, I want to get married? That would be ridiculous. All you want is a date. There is an element of tact and prudence in not putting the cart before the horse, but, if you are most interested in a prospective marriage partner, then YOU need to be honest by saying something like I am asking to date you, but my purpose is to see if you'd be good marriage material for me.

I guess saying "i'm not thinking of getting married" might be a good way to get a man to start chasing.  If women act rather disinterested, instead of telling a guy how she wants to get married and how he has to text her all the time, and acts all insecure and clingy, she's more likely to find out if the guy really likes her.  Why?  Because he will start the chase if he's interested.  Most guys prefer to be the pursuer not the other way around. But girls these days seem to be dramatic, pushy and demanding.  

Men, women, dogs, horses and cattle all run and panic if they feel they are being trapped.  To give a chance for a relationship to start they need to reassure the male that there is no plan for entrapment.  Then he can relax and just see where it leads.

Uh....what??  

You do realize that there are plenty of people in this world you don't need someone else to make them happy, right?  Who have goals and aspirations that at a particular moment in their lives don't include a family?  And that's not only ok but healthy because our happiness should never be dependent on others.

Why fixate on those who aren't interested when there are still plenty of women who define themselves by their relationships with others and feel the "need" to get married and have a family?

Because men dont go on dates with women to hear them ******* babble or to get married. Men go on dates to dip their oil rods in girls. You say 'I'm not looking to get married' is gonna peak my attention up because if you arent looking to get married, then you're on this date for the same reason as I am - to **** eachother. So now I'm paying attention and being on my best behavior since obviously I wanna get laid, rather than groan and drivel boring small talk that weve all done a thousand times through the same date wondering if you're here for a long term relationship or not.