If I make a music sharing site where people can upload their own music and sell their music, and my company which made the site licensed the MP3 codec or another proprietary codec to release the music files for sale, does this mean the licenser of the codec could then individually sue each person selling their music on my site, because they don't individually own a license for the codec, even though they are just using the tools provided for by them by a license holder?
That would probably depend on the terms of the IP licence. Does it cover downstream users, or not? If you're a platform, you get (hopefully, if you were properly advised) what you paid for. What you then represent to your downstream users to bring them to your platform should be honest, though. Prospective platform users presumably want to known whether this is a good platform for their business, i.e. IP-sandboxed, reliable, safe, with large footfall.
It presumably wasn't in fact IP-sandboxed. By that I mean that the upstream licensors have been selfish in their negotiations, or the platform doesn't indemnify you against claims, or even at least offer to coordinate a circling of developer wagons. What's interesting to know if whether they've nevertheless held it out as an IP-safe platform; if not, caveat emptor probably applies, and developers are now presumably kicking themselves for not making IP safety a part of their due diligence before contracting with apple, etc, for a platform on which to build their business.
Realities aside, it's tremendously regrettable that indy software developers and inventors are supposed to have to worry about third party IP rights, particularly over their usage of major commercial platforms for their business.
So then, "Patent trolling, it has to be unreasonable to exist."
This shows differences in generational understanding of words. "Trolling" in this case predates the widespread use with regards to Internet behavior and actually refers to fishing.
Just as trolling attempts to mimic a real school of fish, patent trolling attempts to mimic the legitimate licensing of productive patents. The reasonableness of the "bait" is entirely up to those doing the trolling. (And is largely subjective, which perhaps highlights a fundamental weakness of the current patent system.)
This just doesn't make sense.