1. Killing. How exactly will a buddy kill you, short of pre-meditated murder? If such a thing were to be planned, I'm pretty sure it'd be easier to kill a solo diver, than a buddied diver.
2. Air Theft. My air is my responsibility - whether solo or buddy diving. I plan my air for contingencies. I make sure I have enough air to assist another diver, if that is a contingency needed for the dive. If I run out of air, whether sharing or not, then it's my failure. Gas management is an issue that effects solo and buddy diving equally.
3. Distractions. Situational Awareness vs Distraction. That's not specific to having a buddy; there are hundreds of things that can distract you when diving. Cameras being one of the worst things, followed by marine life. The danger of losing situational awareness is equal, regardless of whether buddied or not... and, thus, is a factor determined by the individual diver, not his buddy.
DD... going to clutch at any more straws? ;-)
What? My instructor, a very good one (back in 1973) explained that the most dangerous thing you can run into underwater is a bad buddy. It may have been an exageration, but it has a lot of truth to it.
In many situations, a good buddy is an asset and will improve safety on a dive. However, you indicated that the dangers are the same with and without a buddy.. clearly not true!
The solo diver will forgo some safety provided by a good buddy, but he also will get many benefits (some of which are improvements in certain aspects of safety).
It is not grasping at straws, I will never be shot with my buddy's speargun, if he stays on the boat. I can make a quick, snap decision to shoot a fish in low visibility and not have to second guess where my buddy is. I never have to look around for a buddy when solo, or waste time looking at their air, or waste time and perceptual awareness by trying to communicate a change in direction, change in plans or some other "issue". I do not have to look out for them. In very low visibility, trying to maintain buddy contact can be a huge issue and DOES reduce your situational awareness and this does reduce your efficiency and can reduce your ability to move rapidly and efficiently.
I have never had a buddy kick up the bottom or destroy visibility, when he is on the boat. I have had a buddy run completely out of air on two occasions, in 90 and 100 feet. Ever have a buddy kick you in the mouth? A danger that will NOT happen when solo. Ever have a buddy wander off and you have to go looking for them? Ever have a buddy who is not your physical equal? This too is a potential hinderance and diving with a weaker partner may add some dangers (or limitations at least) when doing a very challenging dive, say in strong currents. I had a buddy who had a regulator failure at 80-90 feet and swam up to me and was near panic and started sucking an incredible amount of air from my octopus. He had no redundancy and my tank was empty when we hit the surface... When diving solo, you only have to worry about you running out of gas, not TWO people or a paniced one that you may not be able to control.
When there are a lot of dangerous sharks around, I prefer to have a buddy when spearfishing on scuba, because it improves safety. In most other situations, a buddy does bring some additional dangers, hinderances and complexities that I am happy to avoid.
I would strongly argue that two good attentive buddies diving in clear water with an objective of staying together is probably safer than a solo diver, but the dangers of solo versus buddy diving are NOT identical.
I started solo diving at 13-14 yrs old almost immediately after being certified, and most of it was in safe diving conditions, but before I was old enough to get a drivers liscense I was diving solo to the rec. limits in cold water with doubles and a drysuit, in the ocean (and no redundancy.. that still kinda freaks me out).