IMO, there's no such thing as freedom of religion as a thing in and of itself; it's just one specific example of general freedoms like freedom of conscience, freedom of belief, freedom of speech, and freedom of association. A person expressing an unpopular - and non-religious - view on a street corner should be just as protected as someone expressing an unpopular religious view on a street corner.
Also, in this particular case, the quid-pro-quo arrangement you describe is already broken. In Ireland, churches generally get subsidized by the state. I'd argue that with government funds should flow accountability to the government.
While I would rather there be no religious interference in government or vice versa, given the arrangement that exists in Ireland, I'd say that religious sermons from the pulpit should be more restricted than other speech, not less. Effectively, this preacher is a government contractor (AFAIK) and should therefore be held to a higher standard than the general public.
Edit: though the way I'd solve this problem is to cut off government funds to churches, not restrict the speech of pastors.