After crossing (verbal) swords with my daughter, I realized that she had (perhaps unwittingly) taught me the real difference between liberals and libertarians.
Libertarians see the world as mostly good. I have heard non-libertarians criticize libertarians for seemingly looking at the world through rose-colored glasses. Perhaps they're right. John Lennon did that, and look what it got him. But libertarians don't deny or ignore that evil exists in this world. They choose to focus on the goodness that's here rather than the evil. The Golden Rule is our mantra: treat others as you wish to be treated. At the same time, we fully acknowledge the First Corollary to The Golden Rule: how you treat me tells me all I need to know about how you wish me to treat you.
Liberals, in contrast, seem much more the realists because they concentrate on the more insidious aspects of modern life. Because they focus on the evil in this world, they develop a particular mind-set: they long to eliminate the evil. While this sounds like a noble pursuit, we know, don't we, that eliminating evil is the equivalent of a Boy Scout 'snipe hunt' or that old practical joke of sending someone to fetch a left-handed monkey wrench. We can chuckle over liberals' naïve crusade to root out evil all the while shaking our heads over the methods they choose. Because most of you are defined as implicitly evil, you must be forced — whether by law or social convention or 'political correctness' — to behave yourselves. You clearly won't do it on your own.
What that means, on a most basic level, is that whenever 'unpleasantness' is detected, another law is passed to correct it, with the predicable result that we now have so many laws that no one can realistically be expected to know — much less observe — all of them. Ayn Rand recognized that, even if only implicitly, and so we have this quote from "AtlasShrugged":
“Did you really think we want those laws observed?" said Dr. Ferris. "We want them to be broken. You'd better get it straight that it's not a bunch of boy scouts you're up against... We're after power and we mean it... There's no way to rule innocent men. The only power any government has is the power to crack down on criminals. Well, when there aren't enough criminals one makes them. One declares so many things to be a crime that it becomes impossible for men to live without breaking laws. Who wants a nation of law-abiding citizens? What's there in that for anyone? But just pass the kind of laws that can neither be observed nor enforced or objectively interpreted – and you create a nation of law-breakers – and then you cash in on guilt. Now that's the system, Mr. Reardon, that's the game, and once you understand it, you'll be much easier to deal with.”
Thus we have ranchers going to federal prison because they moved fill dirt to a place that had been designated as a 'wetland'. Got that? Their own property is now no longer theirs to do with as they choose because someone in a far-off city — possibly someone who has never actually seen the land in question — has decided that some potential evil must be forestalled. Libertarians would have demanded proof-positive that some evil had already happened — accompanied by mens rea, the knowledge that the act being done was evil, or at least illegal.
Libertarians want a society where your actions are presumed to be in the best interests of society until some proof exists that they are not. Naturally robbery, rape, arson, fraud, assault, and murder all carry prima facie the implication that they are anti-social if for no reason other than none of us want to be subject to any of those acts.
There is another aspect to that difference: liberals are prospective punishers; libertarians are reactive punishers. Liberals make laws to prevent bad things from happening (but they happen anyway); libertarians believe in making an injured party whole. Thus, when government went after "Big Tobacco", they extracted a huge fine from the deepest pockets in the industry. Did that fine go toward offsetting the medical expenses of people who had been harmed by tobacco's ill-effects? No, the fine went right into the Treasury's General Revenue fund. Not a penny went to offset injured parties' medical costs.
You can be a reactive punisher with just a county court house: here's where the damage occurred; here's where the trial occurred. To be a prospective punisher, you have to cast a wide net. You have to be able to prospect for evil-doing in all 50 states. It has to be a federal project. People (like libertarians) who propose that all problems should be solved as close to the local level as possible are institutionally opposed to federalizing every crime imaginable. That may be the biggest difference between libertarians and liberals. With the proliferation of laws, there arise many golden opportunities to profit from those laws. Who profits? Senators, Representatives, corporate executives, perhaps. You? Never.
Liberals wail about how evil corporations have seized control of the government, but they can't admit that it was their unquenchable thirst to protect society with a wall of new laws that actually caused what they now bemoan.