Children who grow up poor are even more likely to becomes drop-outs and criminals, regardless of being single parented or not. So does that mean it's even more immoral for a parent to be poor than for them to be single?
The other important question is ... which is worse:
A child growing up in full abuse of the other parent OR even being abused themselves ...
OR
A single parent raising their child in a safe and peaceful environment?
Children pick up what they see from their caregivers ... which is why some people are more prone to cheating and committing battery against their spouse.