There's no tinfoil hat conspiracy against DC movies - that's just a cheap excuse for poor reviews that this movie has received.
The simple truth is that when a Marvel movie has a bad story, or feels cheap, or is of a lower quality than the other movies (I'm thinking of fan least-favourites like Iron Man 2 and Thor 2) they still get fairly positive critical recognition because while they may be essentially worthless fluff, at least they're 'fun' to sit through for non die hard fans/the general public (i.e. the school of thought that most mainstream critics belong to). This is where the misconception of "Marvel brainwashing" comes from, but it's not brainwashing at all. It's just being able to enjoy a sloppy movie because it's still light hearted and offers some good beats here and there in a mostly fun way.
If a movie like BvS, with the tone and execution that this movie has, is perceived as bad by an audience of critics, then they will find less to admire in the film; i.e. they will give it unfairly overwhelming negative reviews - because if they can't, in their opinion, find any worth in the plot, acting or themes in the movie, then they won't have the fun lighthearted moments to cling to and enjoy like they do for a Marvel movie - they'll just find it miserable and depressing, and they'll hate it. And that's what has happened here.
That's how I see it at least. The tinfoil hat angle is laughable.
I don't think that BvS deserves a 28% score at all, that's ridiculously poor.