It's probably accepted because (in the US at least) you need to financially compensate a surrogate a LOT of money, and even then not many women are willing to go through the inconvenience and health risks. A brief search engine checks indicates only a couple thousand babies are born from surrogates each year. In comparison, that's less than 1/10th of the number of sperm donor babies born each year so in the field of genetic dead ends going against God and reproducing anyway, people using surrogate mothers are low on the incident list.