how come christianity is the only religion that believes in the concept of eternal torment? will there be 'christians' in hell?

That shit was invented by zoroastrians. It wad adopted later by christians to create to ultimate mutt religion.

Buddhists get pretty graphic about the infinity of hell realms awaiting the lustful and degenerate. But its all about karma, you are only experiencing the cause and effect of your own karma. This is the real meaning of Repent/Metanoia - change your consciousness to change your karma to avoid the karmic consequences

https://en.wikipedia.org/wiki/Lake_of_fire

to make them afraid of fighting back

It is copium for the weak, who are unable to defeat their enemies in this life.

Should there not be a punishment for being a piece of shit.