We have discussed Tripp and his book under the Book section "Clarence Tripp"
http://rogerjnorton.com/LincolnDiscussio...d-153.html
I would guess that most of us feel the same as you do.
With Lincoln's knowledge of the Bible, he certainly knew that homosexual behavior was clearly condemned (Romans 1:26-27 - read all of Chapter 1 for the full context)
http://www.biblegateway.com/passage/?sea...ersion=NIV
Even though all sin can be forgiven, and Lincoln knew this, it is still highly unlikely that he would ever engage in this kind of behavior. The level of acceptance of this kind of "life style" was not what it is today, and his respect for God and the Bible was to great.