Because it was an era of war when the 3rd Raikage lived. Dozens of kumo nin and others had got caught in sharingan genjutsu, people learned their lessons provided they were from an opposing village.
wth are you talking about, One does not SIMPLY fight without making eye contact.. it isn't something you can just up and do without having a proper technique.. which is why most people, geniuses like oro , who though they fully well know of sharingans capabilities, still look into their eyes... Kabuto is only able to do it right now because as sasuke says, his snakes can sense heat and movements.. if not he wouldn't be able to fight like that..
Once again, what valid manga proof do you have to say the third won't look into sharingan? when more than 70% of manga characters who have lived in the time of uchihas, have all looked into sharingan? Even friken dazno, and he;s one of the oldest characters in the manga
How else do you explain Lady Chiyo knowing not to look into the sharingan eye?