Those on the left that I have talked to see the key problem is that a secret ballot makes it harder to form unions. The reason given is that between the time that the ballot is announced and the time it is held the corporation has time to attempt to influence and intimidate the labor force. The argument regarding intimidation of card holders by fellow employees and union officials is discounted as theoretical and unlikely.
while that may have been true 50 years ago to some extent, and that well-worn argument has been used every year since then, for decades the opposite has emerged! Especially in PA, which, like the textile states of the south, unions have destroyed jobs where the union finally forced its way in, or forced ridiculous work rules and corruption into the organization. A business that has to focus on the 'grievance file' rather than the economy, markets, customers and the other vagaries of competition WILL self destruct eventually...Proven time and again in PA.