i think all the points are good food for thought, but the pros of having a cofounder FAR outweigh the cons.

as long as you do a good job recruiting the right sidekick(s) and maintain a transparent work relationship, you should be able to avoid many of the disadvantages.

more than anything, you're bound to have highs & lows, and a cofounder will be there to pick you up & get you back to speed when things are not going your way.

plus, the journey is much more fun when you have others to experience it with!