Mr Sillars, a former SNP MP, has signed a letter to justice secretary Humza Yousaf urging him to ditch the most-criticised section of the proposed Hate Crime Bill.
Mr Yousaf has said he will “reflect on whether there needs to be changes made” to the legislation – which has already been criticised by the Roman Catholic Church, lawyers and the Scottish Police Federation, as well as several high-profile figures.
Comic Rowan Atkinson, writer Val McDermid and actor Elaine C Smith have also raised fears that Mr Yousaf’s proposed offence of “stirring up hatred” could stifle freedom of expression.
A group including Mr Sillars, with human rights campaigner Peter Tatchell and Simon Calvert, deputy director of the Christian Institute, has urged Mr Yousaf to drop this part of his legislation.
A letter – also signed by Matthew Lesh, head of research at the Adam Smith Institute think-tank, and Stuart Waiton, a lecturer in criminology at Abertay University – suggested if that were to happen there would be “broad support” for the Hate Crime and Public Order (Scotland) Bill.
While the group said it did “not doubt the government’s good intentions” in bringing forward legislation, it added it had “grave reservations about the draft ‘stirring up of hatred’ provisions in part two”.
The campaigners told the justice secretary: “Rather than introducing wide-ranging and unpredictable stirring-up laws, with all the attendant risk and controversy, we suggest that you instead bolster the implementation of laws already on the statute book.
“You would be commended for acknowledging the problems with part two of the Hate Crime Bill and abandoning the ‘stirring up’ offences.
“Without these controversial provisions, other aspects of the bill would achieve broad support.”
A Scottish Government spokesperson said: “The views offered on the bill will be considered carefully and we will seek common ground and compromise, where necessary. It is important to stress that the bill does not seek to stifle criticism or rigorous debate in any way, people can express controversial, challenging or offensive views as long as this is not done in a threatening or abusive way that is likely to stir up hatred.
“The bill includes explicit provisions on protection of freedom of expression.
“England, Wales and Northern Ireland all have laws in place criminalising stirring up hatred in relation to religion and sexual orientation. The law should protect vulnerable groups and minorities, and this bill – which follows an independent, judge-led review and is backed by a number of organisations – will increase confidence in policing to those communities affected by hate crime.
“We will fully consider the views collected in the consultation and continue to engage with key stakeholders as the bill progresses through Parliamentary scrutiny.”
It comes after a poll for the Free to Disagree campaign group found that 87 per cent of Scots believe free speech is an important right, while lmost two-thirds (64 per cent) voiced support for a classical approach to free speech where “words that incite violence” are criminalised.