Here's a plain english reason:
...the right of the people to keep and bear Arms, shall not be infringed.
The SCOTUS has deemed that the first and second parts are essentially seperate rights.
Dictionary.com Unabridged (v 1.1) - Cite This Source - Share This
right Audio Help [rahyt] Pronunciation Key - Show IPA Pronunciation adjective, -er, -est, noun, adverb, verb
a moral, ethical, or legal principle considered as an underlying cause of truth
keep Audio Help [keep] Pronunciation Key - Show IPA Pronunciation verb, kept, keep·ing, noun
–verb (used with object)
1. to hold or retain in one's possession; hold as one's own
bear Audio Help [bair] Pronunciation Key - Show IPA Pronunciation verb, bore or (Archaic) bare; borne or born; bear·ing.
–verb (used with object)
7. to hold or carry
22. to have and use; exercise
in·fringe Audio Help [in-frinj] Pronunciation Key - Show IPA Pronunciation verb, -fringed, -fring·ing.
–verb (used with object)
1. to commit a breach or infraction of; violate or transgress: to infringe a copyright; to infringe a rule.
–verb (used without object)
2. to encroach or trespass (usually fol. by on or upon): Don't infringe on his privacy.
Translation: We get to have guns. Just like freedom of speech,it is within reason, no rocket launcher or missiles. No registration, no conditions except that we have not forfeited our right (i.e.- convicted felon)