Naruto's surname...

[Chaosmark101]

Because the plot is retarded. Not everyone knew Naruto was Minato's son only very few knew that his kid was Naruto. But for some reason, Kushina wasn't hated or exiled at all for being the nine tails jin like Naruto was.
Minato hoped sealing the kyuubi in Naruto would make him a hero in the eyes of the villagers, but they just saw him as the demon fox who attacked their home and took their Hokage away. Not to mention Hiruzen/Kakashi/Jiraiya not taking care of orphan Naruto.
Hiruzen did the most but we don't really what he did for Naruto other than watch him though his crystal ball.

 

[Itachi Edo]

He was always treated as the fox brat and not as the 4th Hokage son. It works well for me..

The reason was so that enemies wouldn't come after him and i would say that the enemy was the masked man that invaded the village.

this!

 

[JENchuuriki]

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At the bottem left panel.

"Since he is.."

"Shh.. We're not supposed to talk about that"

What actually its all about? A clue that they know Kyuubi was inside Naruto?

I check for further info.

Spoiler

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Mizuki tells Naruto the secret he never know about that other people know.

They do not know Naruto was the 4th's child but they did know he has Kurama inside him? HAHA!
(even if they did know, they still ostracize him)

But yeah, it were kept a secret because Minato wants to and the trauma of Kyubi rampaging still exists within the villagers.

BUT MINATO IS THE ONE WHO SAVED THEIR VILLAGE, AND SACRIFICED HIMSELF AND HIS WIFE, EVEN PLACING THE KYUBI INSIDE HIS SON.

KONOHA VILLAGERS ARE STUPID. REALLY.