I suppose it comes down to what story you accept.
If you think the state of the environment is unrelated to the presence of humans (Jeremy Clarkson unfortunately seems amongst the most vociferous of that camp, which never helps) then you’re going to think having kids makes no difference to the planet.
If you think humans have had a large and detrimental effect on the state of the environment, then logic dictates you’re going to think having kids damages the environment.
Personally I’m of the belief that with far fewer humans the world would be a better place, and this is reflected in my desire to not have children. But I wouldn’t use this as a reason to suggest my friends stop breeding. I’d instead suggest the annoyance of their annoying brats stopping them from riding their bikes is why they should stop breeding.
The only time the sprogging of my friends would annoy me is if I was to be lectured for driving a 4×4 or using a tumble dryer or flying somewhere sunny or whatever by a family with more than two kids. Because I do believe bringing more human beings into the world than needed to replace yourselves has and will do more damage to the environment than I ever will.
Unless the hoover falls against the tumble dryer dial and stops it from turning off for ages like it did the other week. Driest, hottest pants ever.