That kind of progression really happened. "Perhaps allowing interracial marriage today will lead to men marrying other men tomorrow". Gay marriage was unthinkable a hundred years ago. The ideas that are acceptable to society change over time and we can't be so arrogant as to assume our current set of values is correct while all the previous ones were wrong and no future ones will make ours look wrong. You can already see attitudes towards drug use changing to the point where Krueger's "drug operations" seem harmless to many people today.