To suggest that small signal cables need no shield is an insult to electrical engineering and all of the hard work that goes into proper design and not just in cables but in any electrical components. Especially in today’s polluted world.I ran Kimber cables for some years and never had a hum problem of any sort. I stopped when I got the Triplanar, as it has its own cable integrated with the arm. In either case, I ran balanced.
With the Kimber, I could easily handle the phono cable and not induce any hum, despite its ground connection being a wire instead of a proper shield.
However I would not expect this to work in all environments as Lewm points out above. Just like sex, drugs and rock and roll, it worked for me but I don't recommend it for everyone :)
If you are running single ended, an unshielded cable will be more susceptible to environmentally induced noise, but common sense applies to this one- cable manufacturers couldn't get away with selling this sort of stuff if it didn't work. If the cartridge is low impedance, its going to be a lot harder for induced noise to get going. Further, if the input to the preamp is a low resistance, the same will be true. The problem areas will be if a power transformer, AC cord is nearby, or if a radio station is close enough to cause problems. In those cases, a shielded cable of low capacitance would be a good idea.