If there's no mining, there's no point of decentralisation. Bitcoin was born to be decentralised, and not be controlled by any Central authority.unnecessary mining needs to be stopped or they to need to focus on utilizing more energy efficient way of using blockchain tech for cryptocurrency. bit coin aren't bad but the way they are excessively mined using energy intensive method is indeed harmful to environment
Cryptos that are centralised and/or have unlimited or close to unlimited supply are bad for everyone. Bitcoin isn't.
To learn why mining is necessary, you need to know the history and importance of Bitcoin. Like I had mentioned above, this is the best place to start learning about Bitcoin and crypto in general:
teachyourselfcrypto.com is a good place to start..