Biermann was not allowed to hold a "speech" in the Bundestag. Period.
Lammert did know that Biermann wouldn't follow the rules when he invited him on his own hook, since he has been known for decades for his anti-social behavior. I saw him on TV several times long time ago, and if one would encounter him in the pedestrian mall, they would consider him a boozy bum.
And to those who defend war hawk Biermann, you should inform yourselves about his views about the Iraq War, which he still holds.
And the Left Party, which is not the successor party of the SED, is the only faction in the Bundestag that never passed a anti-constitutional bill. If I were German I would certainly vote for that party.
Being for the Iraq war doesn't make Biermann's critique of Die Linke less relevant.