Is it ok to want to die?

Ok, to make a long story short, i'm a guy in my mid 20s, who really doesn't feel there's much point in being alive anymore. Lost interest in most things such as playing sport, nights out, college work, etc. I have huge problems even getting out of bed, i rise at crazy hours and go to sleep at an equally ridiculous time. My sleep pattern is totally messed up as a consequence. I've no motivation to do anything anymore, tried gyming it and eating healthy food, all the usual approaches, but nothing works. Neither does talking to councillors. I am more or less void of confidence and have developed a huge sense of paranoia, especially when i'm around people. I've been clinically depressed

My line of thinking is like this, if a dog is in pain, you'd put it down, its the humane thing to do. Likewise if a race horse suffers a bad break, its also put down. So if a human being is sick, and doesn't want to live, why can't he/she also have that option? I honestly feel like i offer nothing to this world, i'm of no benefit to anyone. And i've come to realise that you get absolutely SFA for being nice to people, if anything they'll walk all over you as a thank you.

What can change my way of thinking? Is it ok to think like this?