The way you phrase it is so biased to make the guy look like he's the worst evil person ever.
So I looked him up, and here is what I gathered:
He staunch anti-islam (kudos from me, as ex-muslim, he 100% onto something).
His activism centered around exactly this cause and has been attacked many times by Muslims, funny enough your people care more about "words" but actual violence? That's fine as long as it's against "hate". The funny thing is that these incidents targeted against him, makes his case even stronger: Islam is a violent religion that does not tolerate any criticism and is incompatible the open German/western society, that thrives on improvement.
So the guy's experience, and especially the recent incident, just confirm what he's preaching, Islam preaches violence against those who criticise it, and is incompatible with western culture and if it grows would present a threat to Germany. Christianity is the largest religion in Germany, yet, you rarely ever hear about violent attacks against its critics. There sure must be a reason, no? And before you jump on the "muh racism bandwagon", skin color has nothing to do with it. It's its religious culture of death, because in Islam, it's an honor to die fighting the kuffar for your Allah, so you can get a better placement in heaven and of course those 72 houris. Germany failed at assimilating lots of refugees that came in the last 10 years, and it's effects are showing.
He held up pictures of Goebbels among other things.
Below his wikipedia:
In May 2013, Stürzenberger was acquitted for the charge of having shown a poster with an image and quote of Heinrich Himmler at a demonstration to prove the similarity between Nazism and Islam.[31] He was sentenced to a fine of 800 euros in July 2013 for insulting a police officer by telling him to "Ach, leck mich doch am Arsch",[32] and to 2,500 euros in 2014 for calling Islam a "cancer" on the Politically Incorrect blog, for which he was acquitted in 2017.[33] He was sentenced to a four months conditional prison sentence and 960 euros in 2015 for saying that all Muslims are potential terrorists at a Pegida rally,[34] and to a suspended sentence of half a year in prison in November 2017 for sharing a photo on Facebook of a ranking Nazi shaking hands with the Grand Mufti of Jerusalem Amin al-Husseini.[35] In December 2017 he was sentenced to a fine of 2,400 euros for incitement to hatred, after he spoke of an "invasion" from the Islamic world at a Pegida event in 2015.[36]