The bottom line is that there is no compelling evidence that stevia in any reasonable dosage causes cancer. In fact, it is worth noting that the incidence of cancer in Japan is very low, although stevioside has been used there for over 25 years. And as for the fertility issue, there is nomeaningfullaboratory evidence that stevia has any effect on male or female fertility, nor on the development or state of the fetus. And again, despite a quarter of a century of use in Japan, there is no actual evidence of any negative effect on fertility or any other aspect of health for that matter.
It should also be noted that all of the problematic studies have used purified stevia at levels far, far, far higher than would ever happen in a normal human diet. Is this important (after all, testing for mutagenic effects at high doses is standard procedure)? The problem is that just because it's standard doesn't make it meaningful. Keep in mind that even things that are healthy can become deadly if taken in large amounts. For example, if you have 100 times the normal dosage of protein each day, you will destroy your liver in short order. If you have a 100 times the normal dosage of water, you will die in a single day -- in a rather messy explosion.
The bottom line here is that all of the problematic studies have been conducted on rats and hamsters with absurdly high doses. In the real world, stevia has been in use with hundreds of millions of people throughout Asia and South America for as much as a quarter of a century. We're talking billions of doses and no sign of increased cancer or lowered fertility. If only the alternative sweeteners that the regulators allow could match that kind of track record.