Well, I'll give you my opinion. I wrote the Intervals section, and I admit that I didn't write it well at all. It was one of my first Wiki contribs, and it sucked quite honestly. I would encourage someone to re-write it if they want to, or I will when I have time to mull it over and do it properly. However, as far as the specific point over whether it relates to the article: harmony cannot exist without intervals. When two distinct (by which I mean different) pitches are sounded, the interval between them is what creates harmony. Harmony and interval relationships are inseparable, because they're one and the same. So absolutely, a section explaining intervals is relevant. However, the way in which I went about explaining it in my contrib wasn't so great. Again, I would encourage a competent and learned musician to do a re-write, or wait and I'll do it.  

 I will say one other thing, which is that Wikipedia is a learning reference, and will serve its best use to the public if Average Joe can come along and glean complete information from non-confusing articles. My ideal is this: say a churchgoing person, one who has very limited musical knowledge, wants to learn how to sing the alto/tenor/bass/whatever line in hymns, so that he/she can feel more "one with God" on Sunday mornings. I want for that person to be able to look at this article, and come away with a clear idea of how harmonies work, so that he/she can practice singing them. The oneand onlything which creates the alto, tenor, and bass lines are the fact that they're pitched at an interval to the melody (soprano) line. Again, intervals and harmonies are one and the same. For the large percentage of the population who struggles with learning things "by ear", a comfortably firm understanding of interval relationships is (along with practice thereafter) the magic key to unlocking the ability to "hear" (discern) harmonies. That's why I think it's important to keep the section in question, but to rewrite it.