I am proud to have signed this open letter, arising from recent attempts to punish the "gender critical feminist" philosopher Professor Kathleen Stock. Signing the letter does not mean that I necessarily agree with all or any of Professor Stock's substantive views. That's a separate issue from whether she is entitled to express them without a large number of her colleagues in the academy mobilizing against her and trying to make her and/or her views beyond the pale of toleration. Whatever I might ultimately think about her philosophical views and/or her policy proposals, or about her more general values and attitudes, she should have every right to express them within the academy without hindrance or punishment. She only needs to conform to some very broad standards of rationality and civility - standards that she has more than met, since she's has gone out of her way to be measured and reasoned, and even conciliatory to the extent that anyone could plausibly expect.
It's very pleasing to see so many people signing the letter, including some high-profile individuals within the discipline of philosophy (e.g. Peter Singer as one of the original signatories and Timothy Williamson as one of the many people who've signed since).
I have reservations about open letters, but they mostly apply to letters that involve numerous people ganging up on a colleague with whom they are in substantive disagreement. There's a huge difference between that and an open letter objecting to exactly that practice and offering support, in an hour of need, to an individual who its victim. In the latter case, I'm always open to signing, provided, of course that I agree with the specific detail of what I'm asked to sign up to.
Kudos to Professor Daniel Kaufman who took on the task of organizing this. Organizing academics to do anything - perhaps especially philosophers - is notoriously like herding cats, but Dan did a wonderful job and deserves recognition for it.