Seller's or seller's agents presence during a home buyer's inspection is typically based on 'position' and not 'issues'. (see Gentleman's Negotiations) Ultimately, it comes across as a confrontational way to negotiate repairs and immediately creates an environment of mistrust for both sides. I repeatedly ask listing agents why they suggest to sellers their presence is required. Most times the listing agent implies it's just how they've always done it. I've heard a couple say they are there to 'advocate for the sellers interest.' Repair requests contractually are typically not required to be negotiated at that time. Plus the home inspector is going to document the same items of concern regardless of whether or not the seller or seller's agent agree. Agents can advocate for the seller's interest when the repair request is received from the buyer and refute any items the home inspector listed if need be at a more appropriate time. All parties can call the home inspector at a later time to clarify any areas of concern.
Once, I had a buyer who said very loudly in frustration, "I'm about to spend a $150,000. You'd think they could leave me alone in the house for 2 hours. *!$%# I've only been in it once before for 30 minutes and won't see it again until we close." From that point forward negotiations turned hostile. I've got story after story of this exact same situation. Some have ended with the buyer terminating the contract because they weren't left alone to do their due diligence. Others have resulted in the seller repairing more items and spending more money than they would have had they not been present. From a seller's point of view, it's hard to swallow some one walking around pointing out everything wrong/defective with their house. Much less things the seller doesn't consider 'wrong or defective.' The seller forgets it's the agent's job to sell the house and a home inspector's job to find everything wrong with it. If a buyer wants a seller to be present the buyer can/will ask and the seller or their agent can avail themselves to that request if they want.
Still not convinced? Ok, that's your right but ask yourself this one thing: Why don't corporations, banks, relocation companies, etc... send a representative out to be present during their REO sales? My guess is the attorneys have advised NO. Do you want to be standing in front of a judge or jury explaining why your behavior, actions, or words impeded the buyer's discovery process?