Just a heads-up, libertarian is usually understood, in the american sense, as meaning right libertarian, including so-called anarcho-capitalists. It’s understood to mean people who believe that the right to own property is absolutely fundamental. Many libertarians don’t believe in intellectual property but some do. Which is to say that in american parlance, the label “libertarian” would probably include you. Just FYI.

Also, I don’t know what definition of “left” you are using, but it’s not a common one. Left ideologies typically favor progress, including technological progress. They also tend to be critical of property, and (AFAIK universally) reject forms of property that allow people to draw unearned rents. They tend to side with the wider interests of the public over an individual’s right to property. The grandfather comment is perfectly consistent with left ideology.

And your argument boils down to “Hitler was a vegetarian, all vegetarians are Fascists”. IP laws are a huge stifle on human creativity designed to allow corporate entities to capture, control and milk innate human culture for profit. The fact that some times some corporate interests end up opposing them when it suits them does not change that.