Our home group is working our way through the Sermon on the Mount currently and of the resources I’ve used in preparation, I have to say that Martyn Lloyd-Jones’ is the most helpful. Here is the first part of his commentary on v 11:
It does not say, ‘Blessed are those who are persecuted because they are objectionable.’ It does not say, ‘Blessed are those who are having a hard time in their Christian life because they are being difficult.’ It does not say, ‘Blessed are those who are being persecuted as Christians because they are seriously lacking in wisdom and are really foolish and unwise in what they regard as being their testimony.’ It is not that. There is no need for one to elaborate thsi, but so often one has known Christian people who are suffering mild persecution entirely because of their own folly, because of something either in themselves or in what they are doing. But the promise does not apply to such people. It is for righteousness’ sake. Let us be very clear about that. We can bring endless suffering upon ourselves, we can create difficulties for ourselves which are quite unnecessary, because we have some rather foolish notion of witnessing and testifying, or because, in a spirit of self-righteousness, we really do call it down on our own heads. We are often so foolish in these matters. We are slow to realize the difference between prejudice and principle; and we are so slow to understand the difference between being offensive, in a natural sense, because o four particular makeup and temperament, and causing offense because we are righteous.
– Martyn Lloyd-Jones, Studies in the Sermon on the Mount, p. 112.