Once upon a time people didn't move much. It was not unusual for someone to live, work and die within 50 miles of their birthplace. The major worry when crossing state lines was during the holidays when the police would watch for Pennsylvania residents returning from Ohio with booze which was much cheaper there. Not only would a fine be levied but the cargo would be destroyed. Ouch.
Times have changed radically. People freely move about the country. Educational diplomas are honored everywhere even tho each state determines its own requirements. Driver licenses and car registrations are honored until the person can schedule necessary tests and file paperwork. Nobody needs to get remarried in the new place of residence.
Wait a minute. What's that? Some marriages in Iowa, Massachusetts, Connecticut, Vermont, New Hampshire and DC, not to mention Canada or Spain are not valid in Pennsylvania?
What if you had to pass a test to prove that you graduated from high school? What if your driver license was invalid and you had to give up driving until you passed the test in the new state or using the car until you had the new license?
It's time to pass a federal law making marriage in one state valid in all. If a couple is married, they are married. Period. While individual states may discriminate against who may or may not marry there, they should not be able to discriminate against other states any more than they can say that an educational diploma is invalid from state to state.