If you sign the party's membership pledge ("YES, sign me up as a member of the Libertarian Party. To validate my membership, I certify that I oppose the initiation of force to achieve political or social goals."), you're a member of the party.
There's no additional clause in the bylaws allowing the Libertarian National Committee to refuse or rescind your membership because they noticed that you're Jeffrey Dahmer.
There could be such a clause, if such a clause was approved by a 2/3 super-majority of delegates to one of the party's biennial national conventions.
While my memory is far far from perfect, I don't remember any such clause ever being moved or debated on the floor of any of the seven national conventions at which I've been a delegate.
What does happen, with some regularity, is that a few party members lose -- or pretend to lose -- their shit when they find out that a murderer or pedophile or other evil/violent person (accused or actual) is a member of the party, and demand that the LNC refuse that person's dues or contributions and use its special magical extra-bylawsish superpowers to make them not a member anymore. IMMEDIATELY.
And when they receive the only reasonable answer to such a demand ....
... a sub-set of the previous group accuses the party members who mention the fact that this bylaws provisions is dispositive, and especially those LNC members and officers who decline to rebel against it and humor the temper tantrum, of being e.g. "pedophile apologists."
Unsurprisingly, that latter sub-set is usually composed mostly of supporters of someone seeking election to a "leadership position" currently held by someone who actually abides by the bylaws instead of doing whatever the hell he or she happens to feel like doing.
Also unsurprisingly, the aforementioned sub-set seems to disappear like a dandelion puffball in a wind storm when it comes time to propose, consider, and pass a bylaws amendment that might
I'm inclined to oppose measures which would allow the national committee to purge party members, for obvious reasons. But if such a bylaws amendment was proposed, I'd take a long, hard, look at it and give it due consideration as a delegate.
What I wouldn't do is support or vote for a candidate for any position on the LNC who advocates pulling, or while in office has pulled, these Veruca Salt Governance stunts.