Altos are to sopranos rather like second violins to first violins - nice to harmonise with, but not really necessary. All sopranos have a secret feeling that the altos could drop out and the piece would sound essentially the same, and they don't understand why anybody would sing in that range in the first place - it's so boring. Altos are unassuming people, who would wear jeans to concerts if they were allowed to. Altos are in a unique position in the chorus in that they are unable to complain about having to sing either very high or very low, and they know that all the other sections think their parts are pitifully easy. But the altos know otherwise.
Altos get a deep, secret pleasure out of conspiring together to tune the sopranos flat.
Altos have an innate distrust of tenors, because the tenors sing in almost the same range and think they sound better. They like the basses, and enjoy singing duets with them - the basses just sound like a rumble anyway, and it's the only time the altos can really be heard. That's all there is to it. For one thing, there are never enough of them, and choir directors would rather sell their souls than let a halfway decent tenor quit, while they're always ready to unload a few altos at half price. In their usual perverse fashion, the tenors never acknowledge this, but just complain louder about the composer being a sadist and making them sing so damn high.