That would be shit

This i want it to happen

J1: *turns off J2's light saber during a swing*
J2: "dang it Greg! Again?"*tries to turn it back on*
J1: *rushes with light saber*
J2: *turns off J1's light saber*

Why can't they just force puts their light sabers into their guts?

comedy gold!

Or they could activate them in the pockets of the enemy, cutting their leg off then finish them.

Because each Jedi forges his own lightsaber. It only responds to it's owner's force, which is also transferable if said owner so desires.