Lojack isn't a theft deterrent, it just helps you get your car back if it gets stolen. It's not an alarm system.
I had the same situation with my wife's Chrysler 300, had a "dealer alarm" and they said the same thing. just waited until I was in the final phase of the purchase and had them all worn down and told them "how about you just let me keep the alarm and I won't walk out the door" and they let me have it.
Both dealership installed alarms I have like that work pretty well, no false alarms from motorcycles, etc, go off when they're supposed to... idk.
I will second TrungLam's comment though, get a decent alarm and good install. Nobody want's to be "that guy" with the annoying car on the block with the alarm going off all the time. I have one of those on my block... it's on a Land Rover :facepalm:
EDIT: I got that package that K_C posted for $250 installed on the Fit, i'm glad my guy didn't rip me off too bad.