Well, we're talking about what
should be legal, so saying "as long as it is legal" is really skirting the issue.
@esmith and others argue - at least when it comes to firearms - they should have pretty free range to use whatever they want to "defend" their homes. What I'm trying to figure out is whether they defend this right
only for weapons or if they also think it should apply to other protective measures.
Razor wire can be pretty effective at deterring intruders - and I've never heard of someone using razor wire that was bolted to the top of a fence in a domestic assault - but it's very common for it to be illegal in residential areas.
Same with motion-activated floodlights. Again: effective at deterring intruders and nobody was ever killed by an annoying floodlight shining into their bedroom window.
... but with either of these things, they're often banned on the grounds of nothing more than aesthetics or annoyance. THAT is where the "self-defense" line is for everything but guns.