To me, the situation is not necessarily about ethics, although ethics are important to me. It's about conflicts of interest. You cannot maintain no conflicts of interest if you stand to personally gain in one venture from another venture and by pitting them against another or propping one up on the other.
If I'm a government official, then it's a conflict of interest if I own a construction company and increase budget for specific constructions to give my company a boost. This obviously happens in our government today, but it doesn't not make it a major problem.
The other perspective is one of grifting. It's similar to con men, who just move from thing to thing gathering up chips at the table. These investors and so-called entrepreneurs are just like that. They are interested in upping their profile at all costs. Their investments and companies are just a means.
I have worked in jobs where I need to report stock holdings more than a certain amount. Imagine a scenario where a low-level worker could affect billion dollar companies' stock enough to benefit from by buying their products on the job. Such a scenario doesn't exist, but the conflicts of interest are still tracked. It is much easier for high profile executives to affect price movements, amd that's why it's more, not less, important for high-level employees.