Oh. Ok. I guess I did not understand your first post. I thought the starter motor turning was only occurring when you "hit the kill switch". Now that I understand that it happens all the time, it makes complete sense. It is just what PaXman11 states. The solenoid contacts have welded together. As PaXman11 says, this is usually caused by a weak/dying battery. Do the following:
1) Remove battery from bike
2) Fully charge battery
3) Take battery to any chain autoparts store and have them do a 100 amp load test. Battery will either be good or bad.
4) If bad, get a new battery, fully charge it, and put it into the bike. If good, reinstall battery into bike. Do NOT attach wires to the battery.
5) Put bike in neutral. Double check that it is in neutral. Move anything of value from in front of bike and triple check it is in neutral.
6) Attach red wire to battery positive terminal
7) Touch black wire to battery negative terminal. Does the starter motor turn?
8) If starter motor turns, remove wire from negative terminal.
9) Find the starter solenoid and rap it firmly with a wooden dowel. This is an attempt to break loose the welded contacts. This sometimes works.
10) If rapping solenoid works, then starter motor will no longer turn when you attach the black wire to the battery negative terminal.
11) Buy a new solenoid regardless if rapping it with the wood dowel worked or not. If rapping worked, you can ride the bike while you are finding, buying, and installing a new solenoid. If rapping did not work, bike is not ridable until you install a new solenoid.