That "warning" Janeway put in was a probe in orbit of the planet. That thing broadcasts it's mind rape to the entire system, so before you could even get to that probe. That's about as dumb as putting a large statue of uranium in a very public area, then putting a sign next to it with a warning about radiactivity.
If this was the aliens idea of morality, they're clearly lacking it in any form. Instead of killing innocent people, we'll just violate them and make them completely miserable because of our sins... yeah. Let's have the Neo-Nazi's commemorate their sins by putting people through Holocaust simulators... it's really a tribute... a memorial... what a load of crock.