That assumes the constitution isn't tyrannical or hasn't been conceived at a time where everything was different. It's like telling a slave you should follow the law because it's the law.
What the AfD struggles with is that the constitution enforces democracy. And while this is obviously an instance of the tolerance paradox, prohibiting people from removing democracy is the only way to ensure their rights and freedoms, and most importantly their power to control the government (by voting).
Constitutions exist to provide friction to fast-moving populist votes. They prevent the two wolves from eating mutton after the vote. They are not immutable; they are hard to change, and can limit simple-majority votes.