Main Entry: im·po·tent
1 a : not potent : lacking in power, strength, or vigor : HELPLESS b : unable to have sexual intercourse because of erectile dysfunction; broadly : STERILE -- usually used of males
Just a note, I was using impotence in the broad term. Such as, "I have no sperm, therefore I am impotent."
The two options that i would consider to become sterile would be male birth control and a vasectomy. I would not consider castration, because over the years my testicles have grown on me and I am kinda fond of them.
I would choose that more painful option is because that method is inherently mechanical, and I understand mechanical means of intervention. For example, I don't understand how they induce birth, but I understand C-sections. C-sections are a mechanical means of getting the kid out. The vasectomy does not stop you from making sperm, it just re routes them to a place where they want try and produce off spring you are legally bound to care for. Also with vasectomies you can get them undone, although there are risks.
But one a boarder note, is it a good idea to encourage sexually irresponsibility with the rates of HIV and syphilis one the rise.