I can deny the importance of human experience (the heat death of the universe will erase all traces of our existence and impact) without wanting to kill humans right now.
How did you conclude the experiences of animals matter?
How do you know animals are having experiences?
How do you know human experiences matter?
I don’t claim to have any answers to the above but I’ve never heard a satisfactory answer to these questions other than ‘I just believe it is so’ and if it boils down to my belief versus your belief I have to conclude that neither one of us actually has any idea.