Speaking with the Herald on Sunday, Spear said: "As Chair of Time for Inclusive Education, I believe it is important that we're able to have open conversations about advancing equalities within our society.
"However, the current narrative regarding trans identities and rights have made it difficult to have these conversations, and media sensationalism and misinformation has meant that rather than properly discussing much needed advancements we are now forced to revert to conversation about defending the existence of trans identities and protecting the current rights of the trans community.
"As a woman and a proud feminist, I know that advancing trans rights does not threaten my womanhood or my feminism. That stance is not only shared by this letter’s co-signatories; but by many women’s support services, networks, organisations and centres across the country - who have a long history and solid record of standing up for women.
"Defining womanhood by conforming to strict biological and physical attributes has been fought against by strong women long before my time. To now see some advocate that trans women are denied their rights and their dignity on these very grounds, I believe would be a devastating step back for women and for feminism."
Dame Emma Thompson, musician Lucy Spraggan, MSPs Gail Ross and Rona Mackay, and MPs Mhairi Black and Hannah Bardell are amongst the letter's signatories which include; women's aid workers, journalists and broadcasters, politicians, publishers, academics, third sector representatives, actors, lawyers, and equalities campaigners.
Hannah Bardell, MP for the Livingston Constituency, said: "We all deserve to live our lives free from fear and discrimination. Scotland is a compassionate country, and we must hope that with compassion comes understanding.
"During LGBT History Month I was reminded of the battles hard won by activists and organisations who changed the hearts and minds of those who could not see past their prejudice, those who bought into the harmful argument that difference means danger.
"These attitudes still exist to some degree, it is far from over. But as we continue to work so that all in our community can enjoy our rights freely and fearlessly, we cannot stand by and let those very same arguments, prejudices and tactics be used against our trans friends.
"I am signing this letter because I believe compassion has been lost in the current discourse around trans rights. I’m worried about the impact of this, and that if this continues then true equality for all will remain a pipe dream. There must be space for people to make mistakes and to learn, and for discussions to be respectful and decent. In the interest of justice and of progress, we must learn to understand - not fear - lives different from our own."
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