How does lyman beecher compare intemperance with the slave trade?

Lyman talks about intemperance as something that is to be fought off. It mentions it as something terrible that ruins families and that we should execrate just as we execrate the cruelties of slave trade.

It isn't really a comparison. It more of an appeal to see one as a horrible thing just like we see the other.

In his own words:

"We execrate the cruelties of the slave trade—the husband torn from the  bosom of his wife—the son from his father—brothers and sisters separated  forever—whole families in a moment ruined! But are there no similar  enormities to be witnessed in the United States? None indeed perpetrated  by the bayonet—but many, very many, perpetrated by intemperance."