Slavery is bad period and it is for deranged monsters the old gods who supported it are worthy of the oblivion and if Morrigan
(which is another slavery supporter) will attempt at saving another one i will remind her how to fear the HoF power.
The DR runners are for me immoral because they are saving critters who supported slavery for thousands of years every time they taught their magic to the Archons,i'm not even sure why Mythal wanted one of them but she did not tried to save Andhoral even if Flemeth was around at the times of Gharael.
No it is not bad. Slavery is integrat to a great pre-industrial society.
Greece - slaver society
Rome - Slaver society
Ancient Egypt - Slavers
Mesopotamians - Slavers
And on it goes. In a time without machines, it is slaves that enable an average man to invest more time in mental pursuits, rather than day to day survival.
Even without benefits of Slavery, an Old God is a creature unlike any other, a chance to break out of chantry dogma, a chance for a new viewpoint on situations. It is a being that existed for milenia and can offer many benefits to assist others.