There are definitely trolls out there. Acacia was one of them.
At the same time there are organizations that are viewed as trolls that have legit claims to enforce their IP.
The MPEGLA that collects royalties for h.264 is a good example. Most people who use VLC never pay their royalty. They should. Part of the reason we don't get better video codecs is because the royalties don't get paid and so there isn't reason to do the research into improvements.
Yes, there is WebM, no it is not free of patent issues, but that is another subject, not for this thread. The point of this is that there are many times a patent is needed, and sending collection letters is necessary.