Using nets or arms seems wasteful to me, to be honest; you'd need to bring a new satellite up there for every piece of debris you want to get rid of. Wouldn't it be a lot more convenient to use something like laser ablation to slow down the debris and make it burn up in the atmosphere on its own?
With laser ablation you fire a high-wattage laser as something to turn a very small surface layer to plasma. The expanding plasma cloud imparts an impulse onto the surface it is ablating, which can be used to slow down debris.
