BERLIN — When a German banker and former government official spoke publicly about a unique “Jewish gene,” when he attacked Islam as a source of violence and stunted development and when he espoused genetic theories that evoked the fright of the Nazi past, the political leadership here quickly condemned him as racist and called for him to be fired.

But the banker, Thilo Sarrazin, an executive with the central bank and a former Berlin finance minister, has not emerged as the marginalized hate-monger that the initial condemnation suggested. His book, “Germany Does Away With Itself,” which laments the growing number of Muslim immigrants, contending that they are “dumbing down” society, was released Monday and is already in its fourth printing, with sales expected to exceed 150,000 copies, according to his publisher.

Mr. Sarrazin has set off a painful public discussion here that highlights one of the nation’s most vexing challenges: how to overcome what is widely seen as a failed immigration policy that over decades has done little to support and integrate the nearly 20 percent of the population with an immigrant background. It is a policy that also stokes anti-Islamic sentiment and hostility.

The sensation of Mr. Sarrazin’s book and his unrepentant posture have also provoked something less tangible, but perhaps more troublesome for policy makers here eager to keep the radical right from gaining a foothold as they have in other parts of Europe. Under the cover of speaking truth to power, Mr. Sarrazin has tried to legitimize hate speech, his critics say.