No. Great God! That's not abuse. I am a pretty thoroughgoing Judeo-Christian Ethic conservative, and no way do I think it is immoral for a single woman to adopt a handicapped child.
Unfortunately, in the adoption world there are several descending grades of "desirability" in adoptable children. At the top would be perfect newborn blond-haired blue-eyed singletons of documented healthy mothers. That's the Gold Standard.
Below that, there's Asian infants, light brown infants, black infants, older-than-infants, children with minor correctable defects, children with moderate defects, and sibling groups.
And last (Lord have Mercy) down at the very bottom you have older-than infants with serious disabilities, sibling groups from drug-addicted moms, and kids who already have tumultuous emotional and behavioral disturbances.
The kids at the top are easily adoptable. The kids at the bottom, God help them.
The cruel fact is, the child in the hypothetical instance described above, has practically no chance of being adopted by a married couple. Say, a one-in-a-hundred chance. And he faces (in Russia) a childhood with nobody but an overworked, underpaid, and overburdened orphanage staff to give him lap-time, affection, attention, and care.
This little boy is mighty blessed if a single American woman (or a woman of any nationality) wants to come and adopt and love and raise him.
And if this woman at some point finds a man who loves her and the child, and marries her, so much the better. But bless the single woman. Her love for the child is sound and right.