Thats where you're wrong. Mid/Lategame you ARE allowed to hit people with your melee attacks when you're close up, however it wont do much damage. But apart from that its useless.

Earlygame if you try hitting mobs, you'll just push the lane becoming prone to ganks and you'll get harrassed too much for the mana gain to become beneficial. Mid/late game the damage is pretty useless, the mana gain is completely deniable and I find auto attack damage + nether blade completely negligible. By mid game you should have so much mana, you'll be chucking out spells left/right/center. Of course, if you have no spells to use (on cd), then by all means whack the **** out of your enemy.

I COULD NOT DISAGREE MORE WITH YOUR STATEMENT THAT NETHER BLADE IS USELESS. Nether blade adds huge amounts of damage mid-late game, especially on turrets and inhibitors. Other than that i like the guide, although i am not a fan of kassadin builds starting off with mana items, i feel it's unnecessary for kassadin because of nether blade.

Maybe in low elo ranked/normal mejais would be fine, but in higher elo I find it isn't as effective and just makes you a greater target.

Thats why :).
Plus, void staff is better :3, especially if the enemy is stacking magic resist.

Pretty darn solid. Any particular reason you don't stack on him? I find that he's usually an incredible snowballer.

lolllllll nioce bro

+1. Kora's kassadin is pretty pro.