Soooo... If you lived in a country where the state (through a state church, i.e. Germany) can offer a legal certificate of baptism and the free church cannot, you would consider baptism preformed by say, a Baptist church, not legally valid and therefore not valid in God's eyes?
What if that church issueing the LEGAL certificate of baptism, once again, taking the Evangelishe Kirche in Germany as an example, is completely apostate? You would still insist that the certificate must be government issues, i.e. through the apostate church, to be valid?
Essentially I agree with you about following the laws of a nation, except when they go against Biblical teaching. However, I do believe in man-made laws, (Let's look at some of the laws in Soviet Europe.......) and I would not elevate the laws of a nation over the laws of the Bible, even though I understand that we must follow the law, as Jesus' followers, except, again, when the laws go against Him directly.
There is no law, as far as I can tell, that says that a church cannot preform marriages without issueing a legal form of marriage. Nor is there a law that people cannot live together without a legal marriage certificate. So I repeat, if the couple are not breaking the law, the pastor preforming the marriage is not breaking the law, and the couple are in fact, honoring God and their local body, by making a public commitment to each other, in a Biblical context of marriage, I don't see anything wrong with it.