Good question. I suppose one could choose only topics about which one had nothing but positive things to say. here is that style. A blog which has a variety of tones, or is negative occasionally comes across as more human which is more personal. I think this is a plus in the short run, and in the long run, how does anyone’s positive tome mean anything if there is nothing contrasting? I think it becomes hollow, and probably bland as well. Integrity may require being critical at times.
If one has a thematic content which is say, something like “bringing the best of ‘x,y, or z’ to one’s readers,” then all-positive has integrity because all but what you blog about is impliedly criticized!

There are my thoughts on your question. Great site, just keep it up. Essie