You can tell that the quality of the comments (and hence of the community) is going down when you can just by looking at the title of a post, predict the type o

You can tell that the quality of the comments (and hence of the community) is going down when you can just by looking at the title of a post, predict the type of negative comments that you will see inside. However the question (which might not have a satisfactory answer) is whether you can keep the same quality standards while still growing. I think that forcibly keeping the community small can be worse than dilution itself.