That's odd isn't it. I had 12 eggs under my broody, only 6 of which hatched successfully and 5 of them were male. I reckon all the females were in those that didn't hatch!
I don't consider it odd, I consider it the odds. This table may help explain it.
1 egg - 1 in 2 will be all male or all will be female
2 eggs - 1 in 4
3 eggs - 1 in 8
4 eggs - 1 in 16
5 eggs - 1 in 32
6 eggs - 1 in 64
But you did not get all males, you got 5 of 6. The odds of that are 6 in 64 times. You have just over a 9% chance of getting 5 males out of 6 eggs when you hatch. The odds are the same you will get all girls. I don't consider that strange at all. I once had 7 pullets out of 7, a 1 in 128 chance. Less than 0.08%.
These odds are the same if you order straight run chicks from a hatchery if you truly get a straight run.
Please help me come to terms with it.
We all have our own set of beliefs and values. Yours are just as valid as mine. I raise mine to eat. That does not make me any better or worse than you, just different.
Others have gone through giving them a good life until they have that one bad day. Make that as quick as you can. They have had a better life than most other chickens. I don't know if that helps you or not. I do not enjoy taking a life but if I'm going to eat them I have to. I try to make that as sure and painless as I can.
When I butcher mine the parts I can't otherwise use are buried in the garden or orchard. That way they feed my plants. Would it make you feel better if you knew they were going to be of use this way. Part of the circle of life.
If you deal with living animals you will deal with dead animals. I've had dogs put down when they outlived their quality of life. It was not easy but it was time. When I trap a predator I kill it. I'm not going to take it somewhere and release it to give other people problems or spread diseases or parasites. I don't enjoy taking that life, but I feel it is necessary to protect my chickens and my garden. You could not keep your cockerels. You tried to rehome them and could not. You did not have much of a choice but to remove them. You dealt with it the best way you knew how.
I've been keeping chickens as pets for many many years, and hatching chicks to renew my little flock and rehoming roosters and any flock members that don't fit in.
How strongly are you affected? Does this make you want to stop hatching? This could happen again next year. I don't know how it works in the UK but when I buy chicks in the USA I buy sexed chicks. You can still get an oops but those are fairly rare. Something to consider.
Would it make you feel better if you contacted a zoo or animal rehab facility and let them use your excess cockerels to feed their animals. It might take some work to find someone that would take them but at least you would not have to do the killing.
I don't know if any of this helps at all. We all have to find our own way. Good luck!