If the party is actively working, in a combative and aggressive manner, to damage or destroy the democratic constitutional system in Germany, the constitution allows for this party to be banned.
Popularity isn't a limit here, at least not in this direction. If the party were irrelevant, it would prevent the ban since the party would not be able to achieve those anti-constitutional goals anyway.
“party is actively working, in a combative and aggressive manner, to damage or destroy the democratic constitutional system in Germany”
You declared it, so it must be true.
If people dont want democracy they should be able to choose so. Its clear that democracy has proven its failure for long term planning and useless bureocracy.
If the majority of German voters want "to damage or destroy the democratic constitutional system in Germany", then is it not their democratic right to do so?
You're not protecting democracy by not letting people vote for the only party that even pretends to care about their concerns. If you want people to vote for other parties then those parties should change to serve the people again instead of trying to make the people serve them.