"Therefore, I said to the children of Israel: None of you shall eat blood, and the stranger who sojourns among you shall not eat blood."
"The blood of a domesticated or wild animal, whether it is a pure or impure animal, is forbidden. This includes the blood of an embryo (shalil), but the blood of fish and locusts is permitted."
(Shulchan Aruch Y.D. 66:1)
The Gemara (Talmud, Chulin 109a and 120a) features an argument between Rashi and Tosfos as to the Kashrus status of cooked blood.
Rashi maintains it is forbidden by Torah Law (D'Oraisa).
Tosfos argues that it is forbidden by Rabbinic Law (D'Rabbanan).
(Of course, everyone agrees it is forbidden!)
However, a liver which comes from a non-kosher animal or which came from a kosher animal which was not ritually slaughtered properly, is forbidden by Torah Law according to all opinions.
Therefore, your local Rabbi of that town is to be praised.
He is the expert on the ground who knows what people in his town will most likely do. If he fears people will seek non-kosher liver, and he can save them by offering raw, kosher liver instead; then it is the best approach to offer the uncooked kosher liver.
This is because the one buying (eating) non-kosher liver is certainly transgressing Biblical Law (even if cooked!). The one who buys raw kosher liver may broil it properly and eliminate the blood; or may wrongly transgress, and ignore that chore. But, even if he cooks the liver with its blood without broiling (searing/kashering the blood) first, the maximum he is violating is Rabbinic Law when he eats it. This is because he relies on Tosfos over Rashi to avoid Biblical punishment; since he is only eating cooked blood, not raw blood.
Similarly, eating Biblically forbidden food is worse than unkoshering a pot on a Rabbinical level.