We don't need a fatwa for that. Isn't piracy theft? And theft is forbidden. So Piracy is haram?
Not really - copyright was developed in about the 18th Century as a means of encouraging people to write about stuff and publish it. Up to that point, if you wrote something there was no law stopping people from copying it.
In England they decided that if a monopoly on any earnings from the copying of something was granted to people, an incentive would be created to publish stuff - encouraging the dissemination of ideas etc. (It was developed in France in a slightly different philosophical way - as a concept of being "part" of the artist/writer) It was originally granted for 5 years only and was only granted if the person who sought copyright actually published the thing (as opposed to someone who wrote something and then refused to publish it - this happens today where for example a writer dies and his family refused to print a book or in Germany where the state owns the copyright to Mein Kampf - and won't publish it).
It is important to realise that copyright was originally intentionally granted to people to benefit the general population.
In the centuries since (and in particular in the 20th) vested interests in favour of copyright have expanded the scope - in particular the Music and Film industry. One of the things they engage in is called "reification" (res being the Latin word for "thing") - i.e. making copyright seem more substantial than it is - so they equate the breach of copyright with theft - and talk about "piracy". Technically one cannot "steal" copyright - the closest one can come is to forge a document transferring copyright to oneself.
Again what is important about this is that these organisations are expanding copyright to the detriment of everyone else - copyright used to be granted for 5 years then 50 years from the death of the writer, then 70 years - now up to 120 years. That doesn't benefit the writer/musician - and it means that there are books and music you cannot download for free for example.
By changing how people perceive copyright - not as something which they are "lucky to be given" but rather something that "of course they should have" - they change the discourse from one of
"ok - how many years of copyright should we grant so that it incentivises people to write"
to
"why are we putting limits of any kind on the number of years that copyright is granted?"
Topic: Work in progress (YouTube vids and making them)