I am inclined to agree with your suggestion and agree with OP.
Mr Entrepreneur starts a business with $1,000 of his own capital and manages to grow his stake to $1,000,000. If the only way for him to use the $1,000,000 as collateral for a loan is to sell it and realize the gain, then he doesn’t need the loan anymore and a successful entrepreneur is deprived of ongoing ownership. But by allowing him to borrow on the $1,000,000 and taxing him, he is still able to maintain his share and use a portion of the loan proceeds to pay the new collateral tax. Netting less of the loan proceeds seems preferable for everyone than to force him to sell his stake.
Mr Entrepreneur starts a business with $1,000 of his own capital and manages to grow his stake to $1,000,000. If the only way for him to use the $1,000,000 as collateral for a loan is to sell it and realize the gain, then he doesn’t need the loan anymore and a successful entrepreneur is deprived of ongoing ownership. But by allowing him to borrow on the $1,000,000 and taxing him, he is still able to maintain his share and use a portion of the loan proceeds to pay the new collateral tax. Netting less of the loan proceeds seems preferable for everyone than to force him to sell his stake.