Of course optifine isn't illegal... It just makes your game look better and run faster. If thats illegal I'm not playing this server again.
I'm sorry, I cannot use it without not being able to join a server. I'm sincerely sorry and ban me if you want.
Looks doesn't really matter tbh. If you compare 1.7 and 1.8 block hits, you'll see a huge difference. ;p