Alternate Character Interpretation: Was the translation machine built by the Martians actually effective at translating their messages, making them lying liars, or was it just consistently mistranslating their warnings of impending doominess as messages of peace?
President: He did say 'we come in peace'.
- Or maybe, unable to ever get the machine's bugs sorted out, the human scientists just played a recording at the landing ceremony to cover their own asses.
- Also the Martian Leader's reaction to the President's big speech. Was he just fucking with him For the Evulz, or did he genuinely gain a bit of respect for the president in that scene. Notice how the Martians aren't overtly sadistic or mean after the speech. Maybe they gave him the closest thing to a noble death they could comprehend.
- The novelization gives an answer to the above questions: the Martians are lying through their teeth any time they say they come in peace. Destroying planets is the entire basis of their civilization - it's their reason for living.
- The Martian who killed Danny DeVito's character, he seems to be contemplating his proposal before he decided "ah screw it, I wanna zap him".
- The Martians may be redneck trailer trash like Ritchie's parents, and a Flying Saucer is just like a pick-up truck to them.
- Grandma might not be such a space case - she might just have a uniquely mordant sense of humour.