If you're curious, nature biotech had a good piece last year on different countries' regulations on GMO crops. US regulations are surprisingly lax, but the companies that developed them have a decent amount of comparative and acute toxicity data. Long-term safety is another question:

Of the over 100 peer-reviewed feeding studies done to assess such risks (Supplementary Table 1), the majority are short-term studies on a small number of traits, which would not reveal any chronic effects from long-term consumption of transgenic foods. And, absent food labeling or otherwise tracking transgenic foods, the impact of transgenic foods on those consuming it cannot be known.

Based on the nature of the genes inserted (An enzyme for breaking down glyphosate in the case of RoundUp Ready and a pore-forming toxin that is degraded in the acidic stomach in the case of Bt), cronic toxicity would be unexpected. But the human body is complex and weird, so it's possible that there's an effect that scientists wouldn't predict... That's ground for a bit of debate, but also what OP's link is trying to dispel as extremely unlikely, given their decades of use.

That all said, human toxicity is a different question from agricultural sustainability and economic impact, which are by far the more important questions at this point.