Alexandre Lotte, the author of icsp describes it as a "Small, fast and simple command-line tool to conver calendar exports (.ics files) into TSV/CSV files for easy analysis and usage in broader use-cases."
And so it is.
I had accidentally imported a holiday calendar into my default Proton Calendar, when I realized two very horrible things: (1) I had no backup; and (2) no one really provides tools for removing entries from calendars in bulk. Later, I would add "Proton Calendar doesn't have a versioning system". But then, no one else does either.
I was screwed.
A few minutes (OK, about a half hour) of searching the Internet, and I found icsp: which turned out to be everything its author wrote that it is.