Everyone is entitled to an opinion.
My late grandmother had the opinion that black people were not equal to white people.
Some people have the opinion that homosexuality is repugnant and should not be practiced.
Others still have the opinion that women should not pursue certain careers, or in some instances a career at all.
There are some opinions that are so far beyond the realms of what we as a society consider normal and acceptable that to voice those opinions is against the law.
This doesn't quite fall into that category; however, I believe that it is extreme enough to have been considered highly offensive and likely to be distressing in the extreme to many, as it was to the OP.
I wonder if some of those advocating "she is entitled to her opinion" would have been quite so open minded had the woman voiced an opinion that to treat cancer "goes against nature" if you or a loved one were undergoing chemotherapy, or that to transplant organs went against nature if you or one of your children were waiting for a kidney or similar?
My guess is you would feel just as taken aback, upset and annoyed as this poor woman does. Someone has just told her, albeit in a roundabout way, her children are "wrong" for existing.
OP, YANBU to feel as you do but there's a lot of idiots in the world. Don't let them get to you 