Some people (he alludes darkly - They Know Who They Are) were bringing up the usual old twaddle about the nasty horrid oppressors of Organised Religion who supposedly have been at war with science and Free Thought and True Spirituality ever since Constantine changed his coat - or maybe since the first drooling male priest set himself up in opposition to the wonderful old matriarchy of Goddess Worship - you can take your pick. And they were saying that the disgruntlement with the Da Vinci Code (and its predecessor <>the Holdy Blood and the Holy Grail was due to the Powers that Be in the Vatican (or wherever) trying to keep the peasants down. Just as Evil Fundamentalists in the USA are always plotting against scientists who teach that nasty atheistical doctrine of Evolution.
That's a nonsense comparison. In fact the exact opposite is true. A better comparison with would be the other way round - just as people who actually know something about biology realise that Young-Earth Creationism (YEC) is unbelievable bollocks, so people who actually know something about church history realise that the rehashed old conspiracy theories in HBHG and DVC aren't worth wiping your bum on. DVC & the rest of them piss people off because they see their fellow creatures being fooled by evident nonsense.
Darwin and Wallace's account of evolution was built on many lifetimes of reflective observation of the natural world by themselves and others, since overwhelmingly reinforced by hundreds of thousands of scientists and scholars. The data, and the reasoning, are all there out in the open for anyone who cares to look at them to see what they are going on about. It (in its various "neo-Darwinian" variants) has persuaded almost everyone who has ever looked into it seriously, including the vast majority of Christians who study biology. Even in the USA YECism is a minority pursuit among Christians and almost unknown among those who study biology seriously (most of the so-called "creation scientists" who are scientists aren't biologists and the few who are are more likely to be biochemists than natural historians). Outside the USA YEC is popular with some of the Muslims, but everywhere else its is a sad joke. Alchemy and astrology have more going for them.
The stuff in HBHG and DVC is not like that at all. It is a farrago of old stories cobbled together with no particular evidence base or scholarship. While the authors of HBHG were probably just trying to make a quick buck out of an easy book to write (is a rehash of some old legends that were never particularly hidden or secret at all - if like me you spent chunks of your youth in public libraries reading about myths and legends and dodgier bits of ancient history you had probably heard most of it before), DVC, perhaps by accident, seems to have taken off. It actually persuades gullible people that it might be true - I suspect that's because Christianity is so unpopular and unfashionable at the moment that anyone who seems to refute it is going to find an audience.
Which at least raises the possibility that it could be the basis for yet another crap conspiracy cult, whose leaders don't even believe the crud they are selling their dupes. The world's got too many of them at the moment. OK, its perhaps not as blatant as scientology (a conflation of Elron's less interesting fiction spiced up with anti-psychiatry rants, and some of the same old Gnostic/Cathar stuff that HBHG was into; deliberately concocted to get money and sex for its founders who probably didn't believe their own lies) but its still not pretty.
Most importantly, both books fail the Knights Templar Test. It is a thing universally acknowledged that any conspiracy theory that mentions the Knights Templar is almost certainly bollocks.