You're making a game in the spirit and style of System Shock.
You control a mouse cursor, on the screen. Instead of mouse looking, you click on the baddies to shoot them.
Just like in System Shock.
Left click to shoot. Left click to use the inventory/HUD. Right click to take things/Use things in the world.
There's a very, very good reason why System Shock mapped Shoot to Right mouse, and everything else to Left.
I've closed so, so many text dialogs, by firing in the air like I'm in Trapped In The Closet.