Things tend to break down a bit when utilitarians try to force moralists to adopt their view, or vice-versa. In the end, it should just be sufficient to have some reason to care about the environment.
We lost species all the time, it's a normal part of evolution.
Also, why is it sadder that humans lead to their extinction than when other species extinct each other?
Its "sadder" because its preventable. Humans are self aware and know that we are causing this. If we change our behavior it wont happen.
But let's be clear, right now, we are sh*tting where we eat. There will be consequences for us as a species if we carry on the way we're going. At best our civilization will be greatly reduced in advancement, quality of life, and many will die in the process. At worst we'll join all the other extinct species.
I'm saddened by the pain and death of individual organisms, but not the loss of a species that they make up.
It would be an undesirable state of affairs to see giraffes go extinct in the wild, but zoo populations can maintain themselves and would probably expand to compensate if they were the only populations left.
Today, we have the IUCN, which didn't even exist until 1964, fifty years after the Passenger Pigeon was gone. We keep track of at risk populations and have a vast infrastructure of care facilities and a lot of interested parties and money in keeping species from dying out. We have an interconnected global communication system to always know what is at risk everywhere. Whereas bans on the hunting of passenger pigeons in the 1880s and 90s weren't enforced and few were aware of them it would be much easier to spread information on and enforce such bans today.
The only captive population of passenger pigeons in the early 20th century was at the Cincinnati Zoo, which slowly died off because they only had an unsustainable population starting out of 20. Today, there are thousands of captive giraffes around the world, and the news of their endangerment should promote more preserves to adopt giraffes to make the species can be kept stable if they die off in the wild.