Rav Yaakov Emden: The Kefira of the Wicked Son is in Denying Mashiah
In Rav Yaakov Emden's commentary on the Haggada, he notes that there are 4 problems with the question of the wicked son:
1) Its brevity and terseness
2) That he called it "Avoda" instead of "a statute and law"
3) Not basing it on Hashem
4) Saying "To you"
For the first 3 problems, we can give him the benefit of the doubt, but not for the fourth, and that's what sealed the deal for him, and we therefore consider all four problems real problems.
Now, regarding problem #2, it shouldn't be a problem since the Torah itself calls it "Avoda". However, the Torah only calls eating Matzot "Avoda" - not eating the Korban Pesah. This is why Matzot are eaten for 7 days since there was still a Shibud (same root as "Avoda") to Par'oh until Keriat Yam Suf. It tells us that the Redemption is not complete and that there would be other exiles in which we would be subservient to others. The Korban Pesah, however, represents complete Redemption.
The wicked son's problem was that he was calling the Korban Pesah an "Avoda". Why did he do so? The wicked son considered the fact that we are in exile - even when we had the Beit Hamikdash, but under foreign sovereignty - and is asking: "What is this Avoda of the Korban Pesah? The Korban Pesah represents Redemption, and there is no Redemption! Just look around - there are Greeks and Romans everywhere! We already have an Avoda - a Shibud to the foreign rule. We don't need a second servitude!"
And this is similar to what happened in Hizkiya's Pesah, where he sent for the 10 tribes, who were almost completely exiled, to come bring the Korban Pesah and many of them laughed his messengers out of town. They were basically subservient to the Assyrians - they were going to start another Avoda?! The wicked son therefore removes the yoke of Heaven from upon him, and thereby takes himself out of the Jewish unit.
The truth is, however, that the Korban Pesah represents the Final Redemption, and this is what the wicked son is denying. He's denying that there will be a coming of Mashiah and a Final Redemption in which we will not be subservient to other nations. That is the Ikkar that he is denying [- the 12th Ikkar of the Rambam].
Due to this, he's considered a Mumar and can therefore not eat the Korban Pesah so his teeth must be blunted.
And what brought him toward this statement of mockery against the Korban Pesah? His impatience with having to say all the words in the beginning of the Seder. He wants to eat the meat raw already like a glutton - without roasting it! We therefore don't let him eat that which he craved as measure for measure.
We then tell him "Ba'avur Zeh" - only those who would keep Mitzvot would be redeemed from Egypt, but this wicked son, since he removed the veil and mocked without shame like an Apikorus, he must not have lineage from those who left Egypt or those who stood at Mt. Sinai and therefore cannot eat from the Korban Pesah.