The Australia international has angered many supporters of the Elland Road club with his decision to join the Turkish giants.
Leeds fans Christopher Loftus and Kevin Speight were stabbed to death prior to a UEFA Cup semi-final tie with Galatasaray in Istanbul eight years ago.
Kewell was a Whites player at the time and featured in both legs of the match, receiving a red card for a late challenge in the return fixture in West Yorkshire.
The letter sent to Sky Sports reads: "My love and respect for Leeds United FC and what the club has done for me will never change, not matter what anyone says about me and whatever their motives are.
"My sense of sorrow and sympathy for the families and friends of Christopher Loftus and Kevin Speight will always be with me.
"I felt that it might be a way to demonstrate that I had not forgotten where it all started and I was hoping that in a small way it would help the healing process of the tragedy that occurred on the 5th of April 2000.
"For me, sport should first and foremost be about the love of your game. But equally important is the respect for not only your team-mates but all those who you compete against.
"For this reason I have always objected to any form of discrimination in any sport and football in particular, as that is the sport that is the most near and dear to me.
"To blame the Galatasaray AS club for the tragedy in Istanbul is simply wrong and discriminatory. This is a club founded in 1905 that has a proud history of striving for sporting excellence and it should be given the same respect as any other football club.
"I respect everyone's right to have their own opinion on whatever they like, but that does not make their opinion right.
"No-one has to agree with my views or my choices, but I think it's only fair and reasonable to allow me and my family to enjoy the same democratic rights as expected by those that have been attacking me over the last few days."