He was not convicted of letter writing he was convicted of Disrespecting the Government. In Canada it is called Contempt of Court and is virtually the same crime. Note that the only mens rea required is that you know you have been told to stop and you openly defy the court. Also of interest is the fact that writing letters if they bring the courts into disrepute is also a crime in Canada.
And what do you think our prison officials response would be to aboriginal protesters who want to be treated differently in our jails because they were arrested for refusing to stop protesting the theft of their lands and resources by multi-national corporations.
You don't like the Cuban system so you presume it is illegitimate but in Canada where we have at least as many restrictions on our rights you accept that as justifiable to enhance peace order and good government.
I personally don't like either the Canadian or the Cuban method of dealing with dissidents but you only seem to have a problem when the protests are protesting to bring about a regime change you want.
An intent to bring a court or judge into contempt is not an essential element of the offence of contempt of court. That was decided in R. v. Hill (1976), 73 D.L.R. (3d) 621 (B.C.C.A.). McIntyre J.A., speaking for a unanimous court said at p. 629:
Even, however, if the cases could not be distinguished on their facts, it is my opinion that an intent to bring a Court or Judge into contempt is not an essential ingredient of this office. In Canada the proposition stated in R. v. Gray,  2 Q.B. 36 at p. 40, by Lord Russell of Killowen has been accepted. He said:
Any act done of writing published calculated to bring a Court or a judge of the Court into contempt, or to lower his authority, is a contempt of Court. That is one class of contempt. Further, any act done or writing published calculated to obstruct or interfere with the due course of justice or the lawful process of the Courts is a contempt of Court.
These words have received the approval of the Supreme Court of Canada in Poje et al v. A-G. B.C. (1953), 105 C.C.C. 311 and in Re Duncan (1957), 11 D.L.R. (2d) 616. In my view, they express the law as it now stands in this country.
The word "calculated as used here is not synonymous with the word "intended". The meaning it bears in this context is found in the Shorter Oxford English dictionary as fitted, suited, apt.....
 As to the mens rea of the crime of criminal intent, the law was neatly summed up by Hill J. in R. v. Peel Regional Police Service where at page 17 he stated:
The mens rea of the crime of criminal contempt, the intention or mental state of the alleged contemner, may be wilfull or knowing behaviour or reckless disregard or indifference that the conduct at hand would tend to undermine the authority of the court: United Nurses of Alberta v. Attorney-General of Alberta (1992) 71 C.C.C. (3d) 225... As stated by McLachlin J. at 253 of the United Nurses of Alberta decision:
Therefore, when it is clear the accused must have known his or her act of defiance will be public, it may be inferred that he or she was at least reckless as to whether the authority of the court would be brought into contempt.Quote:
Zapata jailed since March 2003, had gone on a hunger strike to protest against prison conditions which denied him the choice of wearing white dissident clothes instead of prison uniform.