I blame Walt Disney.
The fact is that that zoo is part of the European Conservation and that giraffe was not suitable for breeding anywhere in Europe. The zoo in Yorkshire that offered to home it already had his brother, so that would not be suitable either.
Animals cost an awful lot of money in feed and vets bills and this giraffe had no useful purpose to the conservation project.
In the wild giraffes are common prey for lions and tigers. I see nothing wrong here. Look at all the culling in the UK - the dartmoor ponies, the wild deer herds etc are all managed to ensure the herds stay healthy. Management includes culling.
Male calves are slaughtered here in the UK because they are no use to a dairy herd and the cows have to keep getting pregnant to ensure our milk supply.
Six lions have very recently been culled in a UK safari park because there were too many of them and they became violent towards each other.
http://www.bbc.co.uk/news/uk-england-wiltshire-26108506
Where's the outrage about that?