The thing is, the majority of genes do a specific single thing. More research on that gene can confirm that yes, it does create that specific protein chain. Then we research the effect of the protein chain either through direct observation or through measuring the effects on the life.
In fact every single plant we grow is attacked by viruses. Many of these virsus inject the wrong dna, sometimes the dna of other lifeforms. You are a million times more likely to die from this than anything a single researched gene will do.
It doesn't matter where it came from if we know what it does. Being scared of it is like being scared of dihydrogen monixide (That's water if you didn't know)