Much more thoughtful and interesting post than many I see on the internet discussing sentencing.
IMO the interesting aspect of this isn't things like comparing what someone might miss out on through being in prison with what they deprived their victim of, or whether a murderer would be a fit and proper person to be a parent. It's more about whether, and if so, how, we might account for the differing impact of a sentence depending on the characteristics of the offender, and perhaps particularly when they're protected characteristics like sex. I don't know how much this is already taken into account with sentencing.
If you imprison a 24yo woman for twenty years, I guess it's true that there's this additional impact on her compared to if you imprison a 24yo man for twenty years. Seems reasonable to me to have a discussion about whether that unintentional disparity of potential impact is something that should be considered. There's got to be lots of ways that the same sentence might impact one offender differently to another, maybe some more worthy of consideration than others. Someone with young children not getting to see them grow up vs. someone without children, someone who will likely die before their sentence ends vs. someone who can look forward to getting out and rebuilding their lives, someone whose main hobby is hillwalking vs. someone who likes to read, someone with fragile mental health vs. someone who can bounce back and deal with anything…
I think for the most part people tend to feel that if there's some particular thing that's tough about a custodial sentence for a particular individual, well, if that affects that individual, then that's just part of the punishment. I guess you could argue that an apparently equal sentence means that some offenders are getting off lightly compared to others, but the practicalities of fine-tuning sentences for equal impact, going through all the arguments that would be made for leniency here or there, would be a total nightmare. And that's assuming it's even possible to make sentences truly equal in impact, when those impacts are as varied as lost fertility, lost income, mental distress, relationship damage, or missed memories. And the result would be a system that might seem less fair than just giving the same sentence regardless of personal characteristics.
I think even if we decided it was fairer to try to adjust for the impact of a sentence based on an offender's characteristics, it's maybe just too complex to try and account for things like lost years of potential fertility, or many of the other individual factors that affect the impact a sentence has on a person.