look, if you have to explain what you said and you said "i can see why they would disapprove", then you need to quantify your statement.
tell them that "you can understand why they would choose not to come because not all of society has come to accept homosexual marriages. while you have no problem with it, not everyone is as open minded about it, and u recognise that fact"
covers your ass, even covers their parents from being bastards by saying they have yet to pull their head out of their ass
