I think the meat cleavers thing was a deliberate choice on their part. If just wanted him dead, they could have done it in a much less attention-grabbing way, so it's not about what's an effective tool for killing someone.

Also, like Dan said, proper guns* are designed exclusively to kill things. More to the point, they make it really really easy to do so – so much so that even killing someone accidentally is very easy.

I would further argue that psychologically, killing someone with a knife is a very different thing to killing someone with a gun. With a knife, you have to get close, in their personal space, and risk retaliation. With a gun there is none of that – the balance of power is overwhelmingly in your favour.

edit:
oops, didn't realise this thread was so long and that most of these points have already been made :$

Video of it going boom:

http://www.theregister.co.uk/2013/05/24/liberator_3d_printed_gun_catastrophic_failure/

I'll never understand the 'I have a gun to defend me in the street' attitude. Is it still the wild west in the US?

If someone pointed a gun at me, I would do exactly what they say, whether or not I had a gun on me.

So where we at with this 3D printing tech?

Have a huge amount invested in WAAM research at work (welding arc additive manufacturing - 3d printing near net shapes with welding consumables, basically), and they've produced some amazing parts that have met the same quality requirements as forged equivalents.

Very impressive stuff, although I'm not convinced the microstructure is comparable to forged metal and although it's passed the quality tests for forged I remain suspicious that it is worse in some other ways that were not directly testing but could cause unexpected failure later (particularly with fatigue loads).

Any progress on your gun?

Client in heavy industry is supposedly using it to repair and manufacture critical parts for ... critical things. If the marketing is to be believed.

Good question!  I still have a job so I suspect it's not quite there yet, and I really haven't kept up to date on what's been happening with printing metals.  I wouldn't be surprised to see some really cool things happening, the world never sleeps!

I watch a channel on YouTube where a guy repairs stuff by spraying metal particles through a torch to repair damaged parts, that has to be very similar to printing!