The term fertility is defined as:
It colloquially has come to be associated with a state of increase or the ability to produce something (fertile imagination is the first example that comes to mind). Fertility has a lot of emotions tied to it and a lot of spiritual energy attached to it. Deities that are involved with fertility are commonly considered to be benevolent towards man, but I find that to be a case of observer bias. Fertility, as I understand it, extends from the traditional dictates of the definition to the creation of wealth and beyond. Fertility is, in my understanding, creation.
People frequently think of fertility as a positive thing and something that is desirable in their lives. People who are seeking to have children are usually the first ones that we think of when we touch upon the idea of fertility. But this potent spiritual force of generation is equally important to farmers who provide us with food, to anyone who produces goods, and bankers who keep our economic systems functional. When you seek to create something, fertility is what you are attempting to invoke.
Fertility, however, is not strictly a good thing. It can lead to overproduction. Situations where there is an overpopulation of deer, for example, lead to devastating ecological effects on a region and eventually starvation in the deer population. All of this came about because, among other factors, fertility. It is the same force that leads to the proliferation of dangerous technologies by way of fertile minds, fertile hands, and fertile economic conditions. Sometimes, it is better to seek to limit fertility or to seek to render something infertile.
It is my opinion that infertility falls under the same purview as fertility. While modern pagans romanticize fertility and view infertility as a tragedy to be remedied, I think that our ancestors understood the necessity for it. I'm somewhat new to being an active follower of a fertility deity (and I'm not entirely sure that follower is the best term but it's what I can come up with right now) but I don't think that my intuition is wrong on this front. I've seen the effects of excessive fertility in one area are on an ecosystem. And those effects are not pretty, they're actually fairly horrific to be honest.
I've felt the pain of struggling with fertility. As someone who had difficulty conceiving and carrying children, I have known the anguish of the prospect that I could not bear my own child. (And the agony of losing children due to miscarriage.) I try to take a pragmatic approach to fertility, which doesn't always work well with emotions. The qualities of generation that are embodied in fertility must be balanced by the rest of the system or it results in the destruction of the system as a whole. Somewhere, that balance comes from the inability to produce. While I understand the necessity of this, it doesn't make it easier.
Fertility, however, is not a 'feel good' thing. A lot of people want to paint it as such and that is really doing a disservice to this force of nature. People don't generally say that a stone being hard is good or bad with out context, but you find many who do that with fertility. So, I guess my position on fertility is that it is a double edged sword. It is something that one should invoke with caution and care because it is a force that has a mind of its own. Once you set something in motion, it will keep moving in what ever direction it is naturally inclined to move.
Fertility is like pushing a boulder. It may move in the direction you want it to, but it is going to have an impact on the entire area. If you're lucky, your impact is relatively controlled and localized, so that you don't disrupt the entire system. If you're really lucky, then your push of that proverbial boulder is something that encourages the welfare of the entire system. But, if you're not lucky, then you're going to create a problem somewhere down the line with your action, quite likely one you never would have anticipated.