This is a perennial debate for divers and these lists..
You have to balance it all out.
If you have a buddy:
1. He may abandon you. Then you're solo whether you like it or not, and you didn't plan on it. Note that "abandon" only means he's far enough away that if you have a serious problem you can't reach him/her. This is surprisingly close if you're OOA and PARTICULARLY if he is moving away!
2. HE may freak out and endanger you. Your buddy CAN kill you, you know.
3. You may have a problem that simply doesn't change outcomes with or without a buddy. A MI (heart attack) at depth is probably fatal with or without a buddy, for example.
If you DON'T have a buddy:
1. You can get killed by something easily managed if a buddy is there. For example, you could get entangled behind you and be unable to doff your kit to disentangle yourself for any one of a number of reasons.
2. You could have an OOA problem and be unable to surface through an ESA. An EBA could kill you anyway; rapid ascents are dangerous in any event, buddy or not.
3. You could have a problem that is not necessarily fatal with prompt help, but without it you're hosed. Blacking out at depth is one of these; if you don't spit the reg its not immediately fatal, but it will be when your gas runs out!
The bottom line is that ALL the agencies will tell you that diving solo is a death wish.
The TRUTH is that you can manage some of the failure modes with redundant equipment, but not all. With proper management there are risks both ways, and its very, very difficult to say which is the more dangerous.
Complacency kills underwater. If you're complacent because you have a buddy, that's bad. If you're not because you're solo, that might actually IMPROVE safety.
Difficult to make the call here, but you won't find many people supporting the concept of solo diving.
Evaluate what can go wrong, what you can do to mitigate and control those risks, then YOU decide.
After all, its your risk of assuming room (or water!) temperature...
(BTW, I don't solo dive - but I do recognize that there are trade-offs for the risks involved both ways.)