There is no real controversy about embryonic stem cell research; because to say an embryo is a person or a human being is perfectly identical to saying an egg is a chicken or a chicken is an egg. No, a chicken is a chicken, and an egg is an egg. They are two totally separate entities. End of controversy!
Furthermore, one absolutely must distinguish between a human (i.e. a complete human being) and human tissue. Cancer in the human body is indeed human tissue, but you'd hardly consider such substance a person, right?
Lastly, A complete human being consists of body (i.e. the biomass part), mind (i.e. chemo-electrical contents of the brain), and soul (i.e. one's personality). An embryo has a greatly incomplete body, no mind, and no soul; therefore falls massively short of being considered a "person".