Clarifying a Bristol citizen's slave trading past on his statue shows where he stood "politically, ideologically and religiously", a historian says.
Bristol City Council plans to place a second plaque on the statue of Edward Colston underneath the original one.
However, councillor Richard Eddy said the wording was biased and said adding Colston had been a Tory MP was unfair.
Historian Madge Dresser, part of the project team, said a "false picture" of Colston had been presented to the city.
Earlier this week Mr Eddy, a Conservative councillor, said the plaque was an "act of vandalism" and said he would not condemn anyone who vandalised the new plaque.
Ms Dresser said: "I think that is very irresponsible of him, this will be put up in good faith."
The historian added the wording was a first draft and the public would have a say.
"He ought to wait until he sees how we have reworded it.
"It's absolutely outrageous that if you put the full facts to the Bristol public that they should then be invited to destroy it because that is what he is implicitly doing."
'Scourge' to charities
The statue was put up in Bristol in 1895, several years after Colston's death at a time of great labour unrest.
The aim by the elites was to find a common identity for Bristolians, she said.
Although he was a benefactor to some charities, he was a "scourge" to others, as he only gave to charities who shared his views, she added.
"Colston himself identified at a time when political parties were being formed as a high Tory, as someone who liked hierarchy and the strong authority of the Church of England," Ms Dresser said.
"He was so sectarian that even when that statue was being put up, it was brought up in the Victorian times [when it was erected].
"It wasn't a dig at the Tory party, it was accurate about where he was coming from politically, ideologically and religiously."