A bit of thread creep, but the use of words like 'family environment' and 'couple' makes me think you only think of two persons when considering adoption and only contemplate whether a same sex couple should be allowed to adopt children.

A much larger minority excluded from the right to adopt are singles. Considering that in many large cities in Germany about 1/3 of all children though once born in a two person family are brought up by a single parent one could consider that as well.

Wolfgang