Whilst it is always sad to see a cat euthanised, the truth is this is happening every day to unwanted animals, or animals that are not a 'perfect' pet and struggle to be rehomed. The sad fact is many animals are euthanised simply because they were born, or because they are not a popular colour. I hate that it happens, but I cannot save the world
It is also easy to jump to conclusions about the owners but I try not to, because I am not in possession of all of the facts. There are many circumstances that could have led to Cat6 being euthanised, and it may not necessarily be down to negligence or ignorance of the owners.
But even if it was because they didnt have insurance, insurance is not the be all and end all because often the insurers wont pay out, or wont pay out enough - particulalrly if you have made previous claims.
For all we know the family desperately wanted their cat to be saved but could not afford it because their insurance had lapsed, or wasnt of a high enough level to cover the costs. They could be heart broken and grieving for their animal (particulalry if cat6 has been missing beforehand). Just imagine that heartache - your cat has been missing for weeks and you get a call from the vet and your hopes soar because he has been found and is alive. But then you are told the bad news.......
Theres lots of hate here towards the owners, but perhaps they are innocent of wrong doing?
But nice one for taking time in your life to try and do the right thing OP. Its a sad end, but at least you tried.