[Ygorl]

Well, if a mobile unit is willing to charge the enemy army and then run away, shouldn't he be able to report what he saw?

As far as killing those kamikaze scouts, the defender always goes first actually. So, flying defenders, or spellcasting defenders, and sometimes archers, can kill them. The player still gets to watch the scout die, though.

There's also a difference between a scout and a spy. Spies can inspire unrest, but they also give more accurate scouting reports, can report on magic sites, and can report on the defenders of a besieged castle.