I agree with the point that this position just rewards Warren's positions, including his outrageous statements of homosexuality in general. However, Obama has stated, time and time again, that he would try to bring everyone together, so it shouldn't be any surprise he would pick someone such as Warren (who could add ex-McCain supports into Obama's ranks).
Personally, I believe that Obama's choice is not a sign of things to come, but negates the support that the gay community gave to him.
Also, "Fierce supporter of LGBT rights?" That is why you didn't say anything concerning Proposition 8 until the last opportune time...