Is it necessary to reduce population growth or family size?

Thomas Malthus, a couple of centuries ago, postulated that there would be a self-limiting effect of world population, and that limiting effect was food production.

(More recently Russell Hopfenberg suggested deliberately REDUCING food production to limit the world's population "Hey, lets starve some more people".)

It's a curious thing. Where people are poorest and most likely to be hungry, population expands to make the problem worse. In many countries (most of Europe, for instance) the indigenous population (as opposed to that portion caused by mass immigration) is falling, despite food being readily available and cheap.

Studies about 6 years ago (by some committee of the UN) reckoned that world food production would need to increase by 30% by 2025 to keep pace with world population growth. Kinda scary.

Measures to slow population growth are a good idea.

Did that add anything to the answers?

Yes.  In developed countries, people use a lot of resources and produce a lot of waste.  Very few people choose to limit consumption.  In other parts of the world, the population is way in excess of resources such as medical care, fuel, etc.  Most of the underdeveloped world is chronically underemployed.  The best place to see the problem of unchecked population growth is India.