Am I the only one who thinks the sex was unnecessary and harmful?

I don't think it was harmful. This is afterall rated R in the US.

If you saw the interview in the extra features with the director at the screening of the film, you would have noticed the lady that interviewed her, asked this question. I remember she said something like it was because it made them feel alive and distracted them from the horrors of the war. There is your answer. If want more information, watch the interview.

Very realistic. Sex was commonplace in ghettos where many families lived in one room. They had no shame.

"Harmful"?

People/animals often turn to sex in life-or-death situations. It's a way of clinging to the former and shutting out the latter. It's also a primal way of attempting to propagate the species.

And it's great stress relief.

Passion is just insanity in a cashmere sweater!

It was normal. What are you, a Puritan?

People with prudish/puritanical views should be teleported back to the Dark Ages so they won't have to be exposed to it anymore. Therefore, the rest of us who DON'T have a problem with sexuality and nudity could be left alone.

OP misses the whole point of the lessons, both of the movie and the Holocaust. People were being persecuted and murdered, simply because others said they were different, and not human. Director Holland showed Jews having sex to show that they're people, just like every1 else. This was also done in her other Holocaust movie 'Europa, Europa' - another true Holocaust story, where the teenage Jewish boy pops his cherry at age 18, on a train, f#cking a Nazi woman who thinks he looks like Hitler (!). The boy was scared, and horny - in other words, just like any 18-year-old boy would have been. By showing us the sex going on (which was true), she refutes the very thesis of the Nazis and racial discrimination, by showing that even while struggling to survive, the refugees have the most human of emotions & actions. The triumph of the human spirit, under the most adverse conditions.