Liberty, Equality--yes! But Choice? Your Jan. 27, 2007 Leader ("Render unto Caesar") makes a defensible point that we need to preserve our ideals of liberty and equality--often a tough balancing act.
But the Leader misses the point of choice--the great balancer of society. If the state restricts the liberty of an adoptive agency (the issue in question) by forcing it to place a child in environments that (in the agency's view) would endanger the child, we have in fact denied the agency liberty to conduct its business according to its values. Equally, we have denied choice to a person of the same conviction who wishes to place his/her child with an agency of that conviction.
Discrimination would arise only if our society (in this case, people seeking to adopt) had no liberty to choose between an agency that might place a child in a homosexual home and one that would not. A case for state intervention (removing choice) arises only where the custom/activity endangers the population at large--as in the case of public tobacco smoking. No one has made that case against private adoption agencies that have their particular standards. I don't have to choose them if I do not want to.
Does the state force orthodox Jewish butchers to sell both kosher and non-kosher meat? Or would it ban a butcher who sold only jerky? Of course not. That would be Big Brother statism! I have the choice of buying meat from the butcher who has the meat I prefer.
Your comparison of race with sexual orientation is a misleading "red-herring"--which isn't kosher!
I may choose whether to marry white or black, in the same way that I may also choose a church that performs weddings for heterosexual couples --if that is my choice!