BERLIN — When one of Berlin’s most popular gay clubs recently held a fund-raising party for refugees, Vivien Roos took along a group of young Afghans and Syrians.

There had been a long discussion at the asylum home where she volunteers about the wisdom of this idea. But Ms. Roos, a true Berliner who is not easily fazed, was confident that the cultural gap between rural Afghanistan and urban Germany could be bridged.

By and large she was right: The men politely declined alcoholic drinks and mingled happily on the dance floor. It was only when two German men started having sex in plain sight that Ms. Roos rushed her group outside.

“One of the boys asked me, ‘What’s that?’” she said. “I just held my hand over his eyes.”

For many of the migrants, Germany is seen as the promised land: A place of stability, healthy economic growth and, so far at least, a warm welcome.