Well in that line of thinking people believed the world was flat till they "discovered" it wasn't. People also believed that we were the only plant in the universe, now we not only know that we aren't the only plant. We also know we aren't the center of the universe, as was once believed, when the first plants were discovered. A theory is just a theory until it is either proven or dis-proven. So reincarnation is just as plausible of a scenario as Christianity or any other unproved theory that is out there.
Hell Christianity isn't even as plausible because it isn't its own religion. They had to steal other faiths and beliefs' traditions and celebrations to make their religion more digestible to the human race. Take for instance the celebrations Christmas and Easter. They both were taken from pagan rituals. There are many more examples I could give here if you would like....
One was Yule the celebration of the evergreens and the feast so everyone could survive through the winter.
http://en.wikipedia.org/wiki/Yule#Pr...ian_traditions
The other being the celebration of the coming of the Goddess Eostre, the coming of the spring and new life. This is the reason for eggs and the bunny for Easter.
http://en.wikipedia.org/wiki/%C4%92ostre
All organized religions today are based on the belief that their God became human, their god died, and that their god will walk living amongst them again to save the faithful and pure. If that is NOT reincarnation, then what is it? The only religion that isnt based on the Belief of reincarnation is Paganism which most religions today have taken MANY of its celebrations from.
Reincarnation also doesn't mean that you will be coming back to this world or existence as a human either. Like with the Buddhists they believe in rebirth in all forms of sentient life. They reject the concept of an unchanging soul like in Hinduism or Christianity.
http://en.wikipedia.org/wiki/Buddhists#Rebirth
http://en.wikipedia.org/wiki/Incarnation
Further evidence, if your wanting scientific proof, of reincarnation is every time someone procreates they are reincarnating themselves.They are imprinting their DNA and genetics into makeing a baby.
We could go on all day about reincarnation belief. When millions of people believe in religion. Which is another something you can't see, touch, taste, smell, or hear. Till religion and/or reincarnation is touchable with any of five senses it will always remain a belief and a theory.