And the US does not give them arms and financial support for that reason.
the US has continued to provide aid to the palestinian gov't and recently recognized a fatah-hamas unity government that slyly skirts the issue by claiming the hamas-linked ministers are merely technocrats and that they will watch closely and recalibrate as needed.
sources:
http://www.aljazeera.com/indepth/opinion/2014/06/palestine-unity-deal-20146595813966105.html
http://www.state.gov/r/pa/prs/dpb/2014/06/227036.htm#PALESTINIANS
http://www.haaretz.com/news/diplomacy-defense/.premium-1.596621
http://www.ynetnews.com/articles/0,7340,L-4526668,00.html
meanwhile the money flows in and, if you think it's not supporting hamas, you're wrong.