Imagine a world with two different flavors of SP existing on the same Steem blockchain, one that allowed self-voting and one that didn't. Which one of these two flavors would have the higher market value?
Obviously the one where self-voting isn't "allowed", because people would see that platform pays better and has higher overall content quality so they all move there. The self-voting platform will only be left with self-voted spam and no new investors would come. The inflation would eat your STEEM tokens alive.
You really don't seem to get it.
You misrepresent my question to achieve the answer you want. By question involved to flavors of SP available on the Steem blockchain AT THE SAME TIME. So folks could CHOOSE to EITHER by the flavor that allows self-voting AND voting for others or the one that allows ONLY voting for others. Contrary to your suggestion, I'm NOT asking about two different blockchains, one that allows self-voting and one that doesn't. With two different blockchains, we must speculate as to which one folks would prefer. With the former, we already KNOW which one they prefer--they prefer the one that allows self-voting. If they did not, and if everyone agreed with your contention that self-voting leads to less valuable Steem, then people wouldn't self-vote.
I agree that if everyone votes only for themselves, the disaster that you describe is inevitable. But dear friend, you've been around here for over a year and self-voting has been both allowed and generally sanctioned by the community from day 1. The disaster you predict has not happened and shows no signs of happening. People are joining Steem at an exceptionally high rate, the highest ever in fact. Many who join describe it as "addictive". All the stats suggest that retention and time spent on the site are both doing quite well. New people join regularly and successfully earn good money.
In snort, there's no evidence to support the idea that self-voting will lead to the collapse of Steem or that it even hurts the price of Steem. By contrast there's lots of evidence that permitting self-voting helps the price of Steem.