Billionaire Mark Cuban acknowledged that Vice President Kamala Harris' plan to tax unrealized capital gains would "kill the stock market," while insisting that she won't go through with it as dubious CNBC hosts pushed back in a contentious interview Thursday. Cuban joined CNBC's "Squawk Box" on the phone to discuss his support for Harris, revealing that he regularly communicates with her campaign to advise on economic issues. The interview took a turn when Cuban was asked about the Biden administration’s proposal – which the Harris campaign has indicated it supports – to tax investment returns that have not yet been...