It is not simply a matter of beliefs, it is a matter of legality. If you try to castrate your own dog for the sake of saving $50 and it goes wrong, you can be prosecuted for cruelty to animals.
Just a few examples of what can happen:
If any hair is caught up in the band, the dog will lick and bite at itself causing sores and infection. The dog can contract Tetanus.
If any part of the abdominal wall is trapped in the band, you will create a hole into the dog's body cavity.
If the band is not the correct size, the dog can develop gangrene and sepsis.
If the band is around part of a testicle, the dog may not even be sterilized. The dog will then need professional castration.
That $50 pales in comparison.