Actually, the idea that Luke's account is Mary's geneaology, does have a few supporters, but essentially the only reason these 'scholars' feel the need to come up with these theories, it that they aren't propared to accept that the Bible has a fair few mistakes. I doubt whether you'd find a scholar who doesn't hold to the idea of Biblical inerrancy (or near-inerrancy) who would give the idea much credence.