Scientists don't make conclusions based on lack of evidence. We need proof they're not harmful to us and the environment. We don't have that proof.
You cannot prove a negative. What you can prove (and what already has been proven) is that all of the GMO crops are safer than peanuts, penicillin, and organic bean sprouts and spinach, and cell phones (GMOs 0 deaths with 100s of millions of exposures over nearly 20 years, the others many thousands of deaths between them due to anaphylactic shock, e. coli, driving-while-texting, etc) .
I am not arguing that there is no risk with GMO technology. What I am saying, however, that the rational approach is to formulate scientific hypotheses regarding risks such that those hypotheses can be tested via either examining existing data or conducting experiements that quantify the risk such that it is possible to determine whether those risks are acceptable based on our best current knowledge.
The "poison" genes you're referencing (e.g., Bt11) are currently based on proteins that are produced by soil bacteria, bacteria naturally found in milk, and other things that humans have been consuming for centuries and that are in many cases applied to organic crops as well. They have also been tested according to both USDA and EPA regulatory standards (in the US, pest control GM traits are regulated by both agencies whereas herbicide tolerance traits are only regulated by the USDA). At this point it is not a question of whether or not they have been tested, but whether they have been tested to a sufficient degree. My personal opinion is that given that they have been tested (both scientifically in controlled experiments and by default through market exposure) far more thoroughly than anything else I consume short of pharmaceuticals, I am OK with them. Beyond my personal comfort level I would challenge anyone to come up with a scientifically defendable justification to require greater testing that would not logically require much greater testing of non-GM foods as well.
The problem is not that there is a lack of "clear thinking" regarding GMOs. The problem is that the ratio of rational thought to irrational thought is unfortunately very small, and the ratio of rational communication vs. irrational communication regarding the issue is even worse. These difficulties are also compounded by the unfortunate fact that many people conflate GMOs with IP laws, religious beliefs, personal philosophy, etc.