SImple terms? The choice resides with the individual, not the Government.
You feel the Government's main role is to provide and maintain social services, support a free market and that's it. Minimal state intrusion in social and personal economic affairs. No nanny state bullshit. As Anarchists believe in NO government, Libertarians believe in some government, with a small g.
A LEFT Libertarian believes in paying taxes towards social services, healthcare, national security, education and the like, but that is ALL you are willing to contribute towards. Projects like HS2 aren't part of taxes you're likely to be prepared to pay for, unless you yourself agree with the idea.
A RIGHT Libertarian believes "my money is my money and I should be able to decide what social services I support and how much I wish to financially contribute". All taxation is theft, as it is taken from us without our consent and we have little say in how it is spent or what it is spent on, especially if a Government we don't support is elected.
I'm a centrist Libertarian, so i'm kind of in the middle. It's not exactly a mindset of "for the good of the nation", it's mostly putting individuals first, about respecting the will and sovereignty of the individual over giving the state power, but that the individual is free to give that state as much support financially and politically that they wish. The hope being that people who are free to contribute to causes they care about will do so willingly, but the aspect is that nobody is forced to do so by the Government through taxation. It's our own choice, not one forced upon us.
Examples; I hate marajuana, the smell is revolting and I cannot be near anyone who smokes it. Should it be legalised? Absolutely. Who am I or the Government to tell free thinking, consenting adults what they do or do not put into their own bodies. It's our choice. They gave give health warnings and risks, and we are free to take heed or ignore them.