To own/rent land are in many ways similar to own rent a house or apartment in RL.
You dont want unknown people randomly lurking in your garden or outside your door. Its creepy in RL, so why wouldnt it be also in SL?
But yes, that landowner reacted overly dramatically. Its easier to set up an orb, covering the private altitude only, and make the rest of the land open.
The "guest" will be informed about trespassing and will be given x seconds to leave. Easy peasy, no interaction/communication needed. The orb is doing the job