"Card check," unionization, an idea whose time should never come

In this day and age, in this country, unions are a dinosaur that should have long ago died away. That sadly has not happened and is not likely to happen any time soon. In fact the aged beast that is unions is trying to make an end run around extinction by attempting to get the legal right to not hold secret voting for unionization.

The current rules are basically that in order to unionize, 51% of the employees affected by the unionization have to sign a petition in favor of a union. Then a secret vote is held and if the majority vote in favor of a union, so be it.

In a number of cases, for a number of reasons, a petition for a union does not always result in a union. There can be a number of reasons for this but the one that seems most plausible is that people can easily be strong-armed into signing a petition as most of the signature collection efforts take place in the open where employees congregate and so there can be a bit of social pressure to sign up. But once you are in the voting booth, behind closed doors with no one strong arming you, many vote against the union that they may have felt pressure to publicly endorse. This is called democracy. This is not good enough for unions. They want this public, potentially (likely) coerced collection of signatures to be the same as a secret vote and once 51% have signed, allow unionization.

What would be the result of proposing that general elections be held this way? If it is not good for general elections (for obvious reasons) then why is it good for unionization votes?