This is irrelevant without knowing whether the species harmed are common pests. If B.t. toxins cause damage only to pest insects, but chemical insecticides cause damage to harmless insects, then the argument is strengthened.

This doesn’t mean there is any insect for which no B.t. toxin is effective. It’s possible that every pest insect can be targeted with the appropriate B.t. toxin.

This is irrelevant without information about whether chemical insecticides do the same. If neither substance does damage to such weeds, this offers no contrast.

This is a reason why B.t. toxins may be less effective than chemical insecticides in practice. Despite their advantages, B.t. toxins are more likely to be repelled by genetic resistance, and thus less likely to work.

This states no difference between B.t. toxins and chemical insecticides that would suggest B.t. toxins are less effective or riskier than chemical insecticides. The author does not say the use of chemical insecticides harms mammals or birds.