[MrEdd]

Getting someone so drunk they don’t know who is around them and then having intercourse is several thousand fathoms deeper than seduction. The sin of the daughters is pretty much in line with what they learned in Sodom

[Vigilanteman]

Context is important here. The mother was gone (turned to a pillar of salt) so was obviously unable to reproduce. The daughters thought they and Dad were the last living people on earth, so survival of the human race depended on an act which they thought necessary.

Since Dad was not going to do it voluntarily, getting him drunk was the only available option. I wouldn't be too hard on the daughters here. They were nice enough girls to be saved out of Sodom.