General considerations about sharing referee reports
It is not common in my field as well to publish the referee reports. I don't think it is a breach of confidence of the anonymous referee; (s)he remains anonymous anyhow. My guess is that scientists are human too, and when they receive criticism of their work they want to get it over with as quick as possible and then forget about it...  

There are arguments for publishing all referee reports: An article does not become "scientific" because it is written by someone with a PhD or someone employed by a university, but because we give enough information that anyone can reconstruct how we reached our conclusions. Referee reports are part of the process, so being open about them would fit. 

However, I would consider it unprofessional to selectively share referee reports. That decreases the openness of the process, as now the reader starts to wonder why this report is shared and the others are kept secret.

I have refereed once for a journal (BMC Medical Research Methodology) that had a policy of publishing the non-anonymous review reports with the article. I actually liked that process: there was interaction with the authors to make the article better. What is important for this question, is that that interaction is public so the reader can see the development of the article.