1) Except for when the tax man comes around - Not legally married, no tax breaks.

2) Except for hospital or medical emergencies as you can be excluded as not being the legal spouse. Then that means everyone is excluded

3) Then there is the trauma to the Children, who have a different last name than one parent or the other. Oh the drama

4) Then there Comes the Inheritance issues. Not a legal spouse means no inheritance with out a will and more legal expenses and delays. Think outside the circle. Try to research and again who steals the inheritance? Isn't stealing a crime/ Ever hear of a will?

5) A "pastor" who does not know or ignores Romans Chapter 13!
1 Obey the rulers who have authority over you. Only God can give authority to anyone, and he puts these rulers in their places of power. 2 People who oppose the authorities are opposing what God has done, and they will be punished.
and especially verses:
5 But you should obey the rulers because you know it is the right thing to do, and not just because of God’s anger. Obey which rulers the local administrative judge, the Federal Judge, the President, the police, the governor.... I could go on a big list of titles that man gave themselves.

6 You must also pay your taxes. The authorities are God’s servants, and it is their duty to take care of these matters. 7 Pay all that you owe, whether it is taxes and fees or respect and honor. Should In pay taxes to Japan Spain, USA, Iraq, Israel, Russia or fill in the blank?

That would include getting a "marriage license".

This is such a bad idea, I can't believe a "pastor" could be that foolish. Well, he will answer for his arrogance and disobedience, to God. Listening to you gives me plenty of questions and who has authority over you?