Which is more dangerous: a counterfeit $100 bill, or $100 in monopoly money? When I owned a restaurant years ago, I found out the hard way that counterfeit money was more dangerous, because in the busy-ness of the dinner rush, my employees couldn't tell that it was fake.
This is why "putting aside our doctrinal differences" for the sake of unity is so dangerous: in the busy-ness of life, it's hard to tell the lies from the truth. The closer a lie is to the truth, the more dangerous it is.