It would go a long way to fix the abuses by billionaires if using stock as collateral was treated as a capital gains event.

When stock gains are just on paper, they shouldn’t be taxed. But turn them into money - by selling, or using them as collateral - and they absolutely should be. https://www.reuters.com/business/media-telecom/elon-musk-borrowed-1-bln-spacex-same-month-twitter-buyout-wsj-2023-09-06/