Is it legal to publish a cease and desist letter that I have received?
Generally speaking, yes.
My interpretation of your post is that you published your opinion about a business or businessperson, and the businessperson now is trying to intimidate you or deter you from sharing with others your opinion. The phrase "the actionable statements listed are clearly statements of my opinion" is otherwise unclear. Under defamation law, only false statements of fact are actionable whereas statements of opinion are not. The businessperson is not entitled to your silence.
If your criticism is about the business, the cease and desist letter sounds in unfair and misleading practices to the extent that the business is trying to conceal from the public some inconvenient information that you as actual or potential customer possess. Even if you published as a competitor, your statements would have to be untrue and misleading for these to constitute disparagement. See the Black's Law Dictionary definition of disparagement [of Goods].
For the reasons stated in the other answer, copyright issues are not a matter of concern. It is preferable to publish the letter as is. Transparency preempts confusion as to "I said, he said". By contrast, paraphrasing the letter for the purpose of avoiding an imaginary violation of copyright creates a risk of you inadvertently giving him grounds for a claim of defamation.
That such '… are clearly statements of my opinion' is itself your opinion and, in the circumstances, hardly conclusive.
– Robbie Goodwin Feb 23 '23 at 00:07Your idea of 'merit' seems like shooting yourself in the foot, and getting caught.
If you don't see what I said as being at least as relevant to your case as what might - largely irrelevantly - be purely legal, that's your choice and I suggest even more than the original Question, defending yourself against such blind mistakes is another good reason to consult a lawyer.
– Robbie Goodwin Feb 24 '23 at 20:46If you do, you make yourself at best complicit in that person's offence, if not separately guilty yourself, and in jurisdictions such as here in the UK, quite possibly compound the issue with further charges of conspiracy.
How is 'But Your Honour, he started it' any kind of defence?
– Robbie Goodwin Feb 25 '23 at 00:57