This pivot from “force” in the LP platform to “obligation” in your critique needs an argument behind it. The LP and libertarians more broadly don’t reject the notion of obligation, including an obligation to help others. That would be absurd. What they reject is that this particular sort of obligation, which in the political realm really means providing financial support, can be compelled via state force. That’s why they use “force” in their wording instead of phrasing it as “no obligation” like you do.
This distinction is, of course, something all of us accept implicitly. I have an obligation not to assault you, and it is permissible for others, including you, to employ force to ensure I don’t violate that obligation. I also have an obligation to attend my daughter’s choir concert, but others may not permissibly use force to compel me to attend. (Why are these different? How are they different? Those are good questions, and important ones in the moral and political realms.)
The point is not that libertarians or the LP are right about the impermissibility of the use of state force to compel acting in accord with these kinds of obligations, but rather that they’re not saying what you say they’re saying. If you’re going to argue against another’s position, it’s important that you begin by getting it right.