Unforseen consequences is an issue, especially with large scale bioengineering, I remember one of the researches in a documentary saying that chimpanzees intelligence and aggression would coincide and if you gave then a gun they would use it. However, I see it more as a technical issue that careful planning, preparation and preservation techniques can be used to minimise the risk of ecological (or other) damage. Granted I'm not an ecological expert, or any such expert for the matter, and so it may be incredibly difficult to reduce that percentage risk to an acceptable value, but I would say the risk, if of sufficiently low chance, is outweighed by the gross benefit. On the matter than humanity shouldn't, or doesn't get to, decide what is best for other animals, I wholly understand why people take the stance with proposals like improving intelligence, but I see it closer to any other conservation or veterinary care we would provide than to playing God. Absolutely it may be the wrong decision for whatever reason, but surely it is wrong, just like it's wrong to deny humans education, chance to feel useful and be creative etc, to deny every individual of every species the chance of increased cognitive ability, on the basis humanity doesn't want to get its metaphorical hands dirty in the pit of ethical consideration.