There is a fine line between bravey and outright stupidity, the thalmor sure crossed the line. Their ideal cause properbly any race (even dragons) to make enermy with them, because most nirm population want to exist. So the thalmor is against Dragons, creatures of every corner, any vampires, werewolfs or whatever, any people that want to live, dark brotherhood (they want to exist too), thieves guild, mage guild and countless other organisation out there.
The real question come into play is, how can an organisation that only give elven armor to their troops can magically form several aliances and cripple ,threaten tamirel? wouldnt their ideals cause all race to aniliate them in a flash?