All very true, Duncan, but I think the deterrent effect also has great value. If the dimwit has the choice between a car with built-in immobiliser and one without, I imagine it would opt for the easier target. If that vehicle then runs out of steam half a mile down the road, the dimwit will not be best pleased and willl probably not be prepared to walk away with just a resigned shrug and muttered "Funny old thing", especially if said dimwit is in the company of others of the species who will be inclined to criticise its choice of vehicle for their bit of fun. Stung to shame, it will feel obliged to vent its displeasure with boot and hammer, before departing the scene.
The detterrent effect of a bright orange Krooklock - or the similar solid metal device we had that tied gearlever to handbrake - will encourage the dimwit to avoid disappointment by moving on to a car without any such protection or an immobiliser, so yours will (theoretically) escape damage. Any car, whether fitted with an anti-theft device or an immobiliser - can be stolen, it's just that classics (dragging myself back on topic) tend to have neither protection so tend to be preferred as a target, whether for breaking into parts or just breaking.
We'd better not get into the dilemma of whether its better to take your face-off radio front or satnav home or leave it in the car. There's a school of thought that suggests more damage will be done if it's NOT under the seat or in the glovebox where any well-drilled lowlife could reasonably expect it to be.
What really pisses me off is that this country has to rely upon a political/administrative cabal who apparently cannot be bothered to do anything about vandalism, graffiti, weekend drunken violence, so called petty thieving and worse but are always, always able to find the time, our money and personnel to prosecute all manner of legislated offences involving otherwise law abiding persons.
Given just how much money British national and local governance/quangos/all govt institutions/assorted committees and so on has untrammelled access to, via enforced direct/indirect taxation just what are they spending it on (no need to respond to this it is a rhetorical question). The usual reply from our representatives (sic) and the police is that they lack the budget/manpower (whoops, sorry, person power) to tackle this kind of criminal, anti-social activity yet when the powers that be are challenged or confronted about our corrupted public status quo watch out.
It would be very easy to catch a lot of these wretches by the simple expedient of going out in organised groups during the early hours when much of this kind of thing takes place but even when they are caught and delivered to the courts for sentencing the judges/legal system won't punish them properly if at all, often pleading poverty (again) because they haven't got the manpower, prison facilities etc., etc., or simply due to politically motivated malice aforethought.
You don't have to agree with me or my obviously personal experience based prejudices but am I the only person who finds this (worsening) situation not only totally inexcusable and unacceptable but also surely unnecessary.