The weakness of all the other religions of the world is that they can be easily refuted by digging into the history of their cults. But buddhism isn't like that, it's a spiritual path designed to lead you to the understanding of the truth of this world, and detachment from the world is the goal. Who are you going to attack? The Buddha? There have been countless enlightened beings even before the last Buddha came around. The Dharma? That's like picking a fight against reality itself, are you going to deny actions have consequences and the things of this world are impermanent? Arguing against buddhism is like denying gravity, that's why most detractors have no arguments besides "it's demonic".