OP's problem is that Utah has issued a warrant, not for speeding, but for failure to appear, contempt, or equivalent. This is no longer an argument about whether OP was speeding and how that ought to be enforced. It is simply a question of whether OP failed to appear or otherwise answer the charge. He did not.

OP says that it was a $150 fine and "probably" is now at $500. This suggests that he does not know. A starting point would be to call the court and determine what is owed and determine whether that is payable. If it is, pay it, make certain that the warrant is recalled and be done with it.

If the warrant has been entered, it will show both at CBP and should OP try to rent a vehicle in the US. Beyond unlikely that Utah would extradite from outside Utah but also possible that a rental agency would decline to rent or also possible that the underlying offense is entered wrong and it takes hours to get sorted at CBP. All a potentially unpleasant experience.

The bottom line is that OP chose to drive in Utah and was obligated to follow Utah law. That included appearing in court in person or through a lawyer. One can spend days debating law and morality. That is not what this is about. Practical answer is to pay this and move on.