According to the Abarbanel, the son is pointing out a contradiction: On the one hand, we recline like free people and dip our food like aristocrats. But, on the other hand, we eat "bread of affliction" and bitter herbs. Are we celebrating freedom here, or are we commemorating the slavery?
The answer is both!
"We were slaves to Pharaoh in Egypt, and Hashem, our God, took us out from there with a 'strong hand'..." Tonight we experience the transition from slavery to freedom.