This fallacy occurs when someone states that the middle point or compromise between two extremes must be the truth.
On one end, people believe abortion is immoral as soon as the baby is conceived and the zygote forms. On the other end, some people think abortion is morally permissible until the third trimester. Therefore, it is most likely morally permissible to have an abortion just after the first trimester.
Just because there are two competing perspectives does not mean that the correct answer is caught somewhere in-between. Someone may be correct, and the other person may also be wrong.