First of all, you do not have an understanding of libertarian philosophy (I could be mean spirited here, and say you're trolling for flames, etc, however...) Libertarians do not, on principle, initiate force or fraud against a person or their property. This is called the principle of "non-initiation of force".
"Public" roads are owned by all of us, through our tax dollars. Getting a drivers license is a privilege, not a right. So, when you get a drivers license, you, as an adult, agree to a contract to use public roads where society has set forth rules of use of said public roads. These include common sense issues like using turn signals and only driving in one lane at a time. You also agree to abide by the speed limits, and to not drive drunk.
When you drive drunk, you are initiating fraud against the public. That is a "crime", because you have violated the terms of your contract (to not drive drunk on public roads).
Life is about freedom to make choices, and taking responsibility for the consequences. You are free to make a choice (to rob my place of business, for example), but you must be responsible for the consequences (that I will shoot you).
So, DUI and DWI laws are ok. Seat belt laws, on the other hand, are not ok. That is a stupid law, where the actions for your decision to not wear a seat belt do not harm anyone but you (except possibly your family).
Private insurance companies should be free to mandate, as part of your vehicle insurance policy, that you must wear your seatbelt, or you will not be eligible for their payout in the event that you do not. But it should not be a law, and not wearing your seatbelt should not be "probable cause" for the police to pull you over and search your vehicle.
I hope this answers your question.
You have made your case that complying to seemingly subjective political laws (arbitrary yet inflexible standards for "inebriation", and arbitrary yet under the code-enforcement agent's discrection "speed limit") is a matter of following a contract. You have not made your case that the seat-belt laws are not part of that contract, but are something that benefits the insurance company. By the mere fact that code-enforcement agents and the judges are collecting taxes fines for seatbelt violations should seem to even the layman that seatbelt laws are a part of that driving contract and privledge.
Your claim that driving drunk is "fraud" doesn't meet the legal definition of fraud any more than any legal form of impaired driving is "fraud". So either you need to show how "driving drunk" is indeed fraud, or drop that unsubstantiated claim.
It seems that your primary reason for liking "drunk driving laws" but not liking "seatbelt laws" is that the former is common sense and the latter is just "stupid". This is a fine example of why Libertarianism is just warm-up act for Totalitarianism, for you declare by fiat that one is common sense (even though the declining acceptable levels of intoxication bear little correlation to actual impairment) and the other is "stupid" (just because you may not like buckling up, or that is some aspect of the contract that is too inconvenient and too burdensome).
My primary transportation is a motorcycle so seatbelts are when I cage-up for events where being exposed to the elements is a bad thing. Not only does this Cat 'N Mouse game of life make wearing seatbelts necessary so as not to take penalty points from "The Man", but there hasn't been a single "drunk driving" law that has kept drunk drivers off the road. It is in my interest, my family's interest, my friend's interest, the premium payer of insurance's interest, the emergency crew's interest, my client's interest, and the interests of all of those on welfare that depend on me to work, that I survive a motorvehicle trip across town. That is why I wear seatbelts.
You may call seatbelt laws stupid, and I hate the fact that people are so damned irresponsible, and busy-bodies are so power-mad that the government feels a need to lay down these draconian responses, but as much as you feel that the potential harm that a drunk driver can do merits Gestapo like check-points (where they also check administrative violations like registration, inspection, valid permits, and fish for other violations such as guns, drugs, open containers, contraband, illegal aliens, etc.) I can come up with equally valid reasons to why compulsory seatbelt laws are just as safe and should be part of every driver's legal responsibility.
But you might still just call it "stupid" because seatbelt laws have their roots in the insurance company, whereas head-on collisions caused by drunks must not effect the insurance industry.