Much of my political philosophy boils down to what I view as a commonsense take on the issues.
If the USA requires 'gun registration,' who is most likely to climb in the SUV, drive down to the police station, and register them? Common sense would tell you that people who obey laws (aka the law-abiding) are most likely to do this.
If I'm a thug, why would I bother? If I kill people and/or steal things, thus violating our most basic laws, why would I obey this law?
Gun registration is essentially legal harassment of law-abiding people and would do little to prevent crime. The amount of harm it would do to our rights far outweighs what crime it would prevent.