This isn't exactly an answer to your question, as I do not know what the common belief could be and, as well, without doing serious research through the explora

This isn't exactly an answer to your question, as I do not know what the common belief could be and, as well, without doing serious research through the exploration of blogs, social networks and such to determine what said belief could be, it would be impossible to give a definitive answer. That being said, I don't think Ubuntu is any more or less secure than OS X. This is just a personal opinion.