Can I please have your reasons why you think so, e.G. For or against."should all parents be allowed to select the sex of their child through pgd/ivf? "

Against. Unless there is some compelling extraordinary reason to do so, I am against it. In general, I feel that one of the downsides of human intelligence, is this need to control, control, control. Perhaps we should extract more wisdom from nature, rather than trying to direct and control. There is something to be said for the art of selflessness, as opposed to the actions of selfishness.
Family Balancing. I am in favor of gender selection using the rules of "family balancing" but not gender selection for anyone at anytime. Family balancing is an ethical approach to gender selection in which someone can only qualify in order to balance the number of boys and girls in the family. You therefore must already have at least one child and you can only use the technique to balance or equal the genders.