I have the feeling that any ETI who are unfamiliar with the human
shaped life form will have trouble understanding what is going on in
the scene shown in Contact of Hitler opening the 1936 Berlin Olympics,
to say nothing of comprehending his deeper, darker character.

We could also get into whether an ETI who might understand Hitler
and the Nazis upon receiving more Earth broadcasts on the subject
would still view him the way most humans do. What we think of as
evil and good may be totally different things elsewhere.

For example, the majority of Westerners think it horrible to eat a
fellow human being, but there have been others in history who
thought and acted otherwise. Some even considered it a great
honor, including the one intended to be the main course.

FYI - The other early television broadcast of that era was the
Coronation of George V of Great Britain, but let's face it, that would
have had nowhere near the dramatic impact of getting back a
transmission of Hitler from aliens.

Then again, who knows how an alien mind might perceive THAT.

As for the potential threat of broadcast leakage, most signals
inadvertently sent into the galaxy from Earth are fairly weak and
random against the very noisy natural background radio noise of
the Milky Way. Radar pulses from the military and places like
Arecibo pinging NEOs and other worlds are much more powerful,
but they too are random. Then again, fire enough buckshot....

Even if we kept quiet, which is impossible as there will always be
those sending messages into space (and that will only grow), our
planet can be detected as a place for life even from interstellar
distances by a civilization with the right technology. We just
proved we can detect life signs on Earth with Venus Express
and EPOXI.

Plus hiding under our beds is a good way to make sure we never
develop as a society and species and ultimately make us even more
vulnerable to an alien threats. Though I think with 400 billion star
systems to choose from, it is rather egotistical of us to think we are
the Big Focus of the Milky Way.