"Muh 1st Amendment" is such a weird copout. It only means that saying these things isn't illegal, you can say these things. That doesn't mean they're morally acceptable, or that people have no right to react to it in any way. They also can respond within the confines of law. Like letting your employer know how much of piece of shit you are.
Publicly celebrating killing of someone because of things they said is not fine, even if it's speech protected by 1st Amendment.
Here's some ammo to use against them.
Something that pisses lolbertarians off (has Null stopped being one yet?) is what the US government did immediately after 9/11. We were trying to figure out how to persecute and get rid of Islamists in the US while maintaining within the limits of the Constitution. How do you fight someone who doesn't follow your rules?
It's simple, you don't follow them either. Judge Richard A. Posner is quoted with this line "The Constitution is not a suicide pact." Meaning, in order to maintain law and order and face a threat against the existence of your government and your ability to live peacefully, constantly refusing to defend yourself from said threat because you feel the need to follow the Constitution will eventually result in your entire country being compromised and taken over by hostile forces.
What lolbertarianism fails to address is a country faces an existential threat, it provides no practical means of stopping the threat immediately because it mandates for you to put up barriers to limit government power.
The problem is, again, the opponent doesn't have this limitation. And while you're sitting there bitching about power and claiming you're a "principled" individual, they're shooting your neck off and laughing at you for not responding to them.
Right now, Trump has what Sam Hyde calls the Mandate of Heaven. The reason why Trump went easy on the left is because nobody was ever killed for their beliefs. But now? A majority of the party is giving him and BEGGING him to use the power of the State to go carte blanche on the left that encourages political violence. They are enemies to what this country stands for. There is a clear and imminent threat that a lot of leftists would not hesitate to kill or hire someone or instruct someone to kill you or your family if you have the wrong beliefs and there was no repercussions for it.
That is a very obvious threat. It's hard to stand up for your ideals when they kill you for it. Dave Smith/Ron Paul types are absolute retards if they continue bitching about the use of force for SELF DEFENSE using political powers granted to Trump by the people.