You are wrong. The opt out approach for Union political actions was created by the courts. Congress / state legislatures wrote the laws with no opt out option at all.

However, after numerous lawsuits were filled by non-union members in open shops opposed to political activities that the union was funding with their mandatory fees, SCOTUS declared that this was a violation of the non-member’s 1A rights and that the unions had to refund that portion of the fees used for political activities if the non-members objected.

Horse puckey. It was deliberate – the unions had their minions in the legislatures write it that way.