As a man, I highly agree that parents should start having more girls. It would even out the genders and would also make a lot of men happy in the next few generations. Having more women is beneficial to society because women are tender and caring individuals usually so that would be wonderful.
I think it's a personal preference on what gender you want your child to be, we need both males and females in society in equal numbers so I don't see why we should prefer one over the other, overall parents can't really choose what gender their child is going to be anyway.
I do not understand why parents should be trying to have more girls. In most countries, women outnumber men by 2 or 3 percent. In countries like China, where men vastly outnumber the women, there should be parents trying to have more girls, I think. But in most countries, no.
There is no real way to determine the gender of your child at the point of conception. No matter how many times you try, the likelihood of having a biological girl or boy will always be fifty-fifty. There is a very even division of gender in society, and it is fine the way it is.
I do not see any benefit in parents trying to have more girls rather than boys. The only place I think that would benefit from parents having more girls than boys is in a country like China. The country's rule on couples only having one kid has really caused an imbalance in terms of the population.