City took full advantage, taking just four minutes to open their account through Yaya Toure before Mario Balotelli bagged his 10th goal of the season and David Silva wrapped up a 3-0 win in the second period.
Villa fans were clearly unhappy with the move but Houllier was unrepentant.
"I had to do it and I would do it again," said Houllier.
"I understand where they are coming from but I don't think we could have beaten Manchester City today."
He continued: "Nathan Delfouneso will go to the Under-21 Championships in the summer. Emile Heskey went to the World Cup and Gabriel Agbonlahor was in the squad for Denmark last month but couldn't go for personal reasons.
"Those in midfield are internationals, so were the two centre-backs. We have quality in the squad and we have an important game against Bolton at the weekend.
"I don't think it would have changed anything. We were beaten by a team that is better than us at the moment and was ruthless in terms of goal opportunities.
"They were clinical and you must give them credit."