If that is true, there should exist cards that let you load other assets on them to cover the cost of spending. Like a card that sells your Google stock to cove

If that is true, there should exist cards that let you load other assets on them to cover the cost of spending. Like a card that sells your Google stock to cover the cost of your beer. The ability to sell capital assets without paying tax should make these cards very popular. If these cards do not exist or are not popular, I would take that as evidence that selling a capital asset is taxable, whether or not it was triggered by a card purchase.