I think what most of us are trying to do (though I can really only speak for myself) is not try to force others to believe that animals go to heaven, as neither a belief or disbelief in this is going to have much of an effect on the state of our souls, but rather to encourage a spirit of love and mercy towards non-human creatures. The idea that animals are just things, unfit and unworthy of eternal happiness and incapable of anything other than mechanical, brutish, instinctive actions, opens the door for poor treatment of them. Conversely, the idea that God may actual find these aspects of His creation good, as the Book of Genesis tells us, opens the door for kind and humane treatment of them.
The vehemence some people on this thread have used ininsisting that there is absolutely no way God could include animals in his plans of heaven, and their disingenuous claims that they are being so insistent only for the good of others, is what keeps upsetting me and keeps me in the argument.