There are many plausible explanations for the homeland and identity of the Sea People. Insisting that the Sea People were "just pirates" is a cop-out answer.
Some of the ethnicities mentioned in the Medinet Habu inscriptions are mentioned prior to the Sea People attacks which indicates at least some of them were known ethnicities to the Egyptians.
Texts from Ugarit in Syria strongly support Maspero's interpretation of the texts at Medinet Habu, that there was an organized cohort of invaders in the Aegean. Although the wealth of names mentioned by the Egyptians are absent, one letter from Ugarit mentions the "Shikila people", who may be the Shekelesh in the Egyptians sources. 
We have no reason to doubt these are the same people when many cities in this period collapsed within years of each other across the Mediterranean.
Many ideas about the origins of the Sea People are valid and supported by extensive written sources.