I'm not really being pedantic no, yes you do imply you think that it is good because of course you do, so do I, that's why I said it was a self interest argument. What was missing was an appeal to something else, which would make it not a self interest argument.
Open source does not just mean a race to the bottom on price, it means a race to the bottom on everything, like alignment or refusals. Do you really think the world is better off with open source image and videogen? easy access to revenge porn and misinformation generation? etc.?
They do collaborate, on alignment especially, which is what matters most. Sharing capabilities would do nothing w.r.t. pro-socialness. They do these things because they also, rightly, believe a multipolar future would be dystopian.