Sister doesn't address the reason the sower said not to pull the weeds: because the servants might uproot the wheat; it had nothing to do with determining which was a weed.  The weeds came up as the wheat sprouted heads; that is, it was clear which were weeds and which were the wheat.

The thing about weeds is that the strong plants fight against them and overcome them.  If you pull the weeds, you might weaken a strong wheat plant.  That is, the good become stronger by having the evil among them, overcoming them.  How can good people know what good is unless they have the evil among them?

This parable was not about the servants and their desire to weed; it was about the plants.