Why do atheists seem to use Buddhism as a tool to work against Christianity? Would Buddha approve of that?

Sometimes, I've met some atheists, who use Buddhism, or who marginally study Buddhism, just because Buddha wouldn't say whether he believed or disbelieved in God. Come on, either way, I believe Buddha would definitely have enjoyed Christianity and agreed with many of its ideas, considering both religions share a lot in common. What do you think? Is it fair for atheists to use Buddhism as a tool against Christianity?