Do you think it's acceptable for a 14 year old to have a...sexual relationship with a 17/18 year old? (I don't)

Depending on the state (in the US) it is illegal and the older (of age person) can go to jail and be placed on the sexual offenders list, which would screw up their entire life. Different states have different laws anywhere from an age difference of a few years (an 18yo with a 17yo for example) which is frowned on, but not criminal, to anyone under the age of 18 having sex is criminal (like a 16yo and a 16yo), in which both can be criminal and victim. Best to stay away from it until you're both 18+.

Not only do I think it's wrong, but more importantly, every state attorney general and every district attorney in the U.S. thinks its wrong.

As mentioned both, should wait until each is 18.

A better question would be is having sex with a minor worth a lifetime of consequence

It is not acceptable for a 14 year old girl to have a sexual relationship with anyone. And if she is having one with some who is 18 it is illegal anywhere in the US. With  17 year is also illegal in many places as well.

No. That's why it's illegal.