People who change their minds are often accused of contradicting themselves. (textbook answer)
People who change their minds are often blamed for contradicting themselves. (my answer)
We "blame" someone when we believe that he or she is at fault for an unpleasant situation, while we "accuse" someone when we make a claim or conclude (even without conclusive evidence) that he or she has a certain nature or has done something wrong. I can't say that your word choice is wrong but based on clues such as "contradicting themselves", it is likely that others will decide that these people don't mean what they say (i.e. contradicting themselves) based on their history of changing their minds.
Researchers have come to the conclusion that moderate consumption of red wine has health benefits. (textbook answer)
Researchers came to the conclusion that moderate consumption of red wine is beneficial for health. (my answer)
I would say that "have come" is more appropriate as researchers made a conclusion in the past and the conclusion is still regarded as true now (which is why the research finding is published). In your answer, "is" is a linking verb where an adjective (beneficial) is used to describe a noun phrase "red wine", and your sentence is also correct with a slight modification: "Researchers (have) come to the conclusion that moderate consumption of red wine is beneficial for health."