Normally, people who give up shampoo still use something. They might use a weak baking soda solution followed by weak vinegar (both antibacterial), or use soapnuts, or just use conventional conditioner without using shampoo first.
It is unhygienic to use nothing. This is coming from somebody who has done it, and I still stretch my washes as much as possible. No part of our body has evolved to use soap, that doesn't make it not unhygienic to eschew it. Although, I don't care if people don't use shampoo, and I would do the no-poo thing myself if it suited me. (My scalp will never not be oily, and my frizzy knotty hair will never not need conditioners in order to brush it). Just, there's no point in pretending that using only water to wash anything is hygienic.
Note to Jack: a different opinion to you is not "judging" or "bullying" - especially not on a gossip website that you actively choose to read. The desperation to be victimized is pathetic.