Many people look at magic and assume that blessings are strictly 'good' and curses are strictly 'bad'. Much of what the entertainment industry has presented on this topic has been shaped by the cultural attitude that these two things are true.While cultural belief does shape the metaphysical landscape to a degree, the idea of 'good' vs 'bad is an over simplification and highly subjective. That which is 'good' for one person is not so for another in many cases. That is before you start to consider the implications upon the larger global scale.
As such, I define blessings and curses in a different fashion. Blessings are magic that works to increase an element of a situation. Curses are magic that works to decrease an element of a situation. As such, the spell to increase the population of ladybugs in your garden to combat the aphid problem, for example, is a blessing. The spell to reduce the population of aphids would be a curse. It is with a bit of cleverness and creativity that one can craft a blessing or a curse for any given situation.
Many people argue that certain phases of the moon are the times for certain forms of magic. This is not entirely true. While waxing phases of the moon do correspond with an increasing psychic 'tide' of energy, a curse can still be cast during this time. It will not be as effective as one cast during the waning phase, or the decreasing psychic 'tide' but it will still work if proper effort is applied.
Over the ages, generations of magical practitioners have learned that certain things are true about how one performs magic. Records of this information are transcribed into grimores, tables of correspondences, and recorded folk lore. This information bears out time and again that magic can be worked for increase or decrease of an influence.
There are very few spells that exist for the purpose of maintaining stasis of a situation. This is because life requires there to be movement in all areas. Apparent stasis comes from a slowing of the rate of change, but the changes will still occur. This is due to the fact that change is an inherent part of the fabric of reality. The trick to determining if a blessing or a curse is necessary to achieve one's goal is the same as that for observing anything.
One must compose their frame of reference and operate within those parameters. In the case of the aphid problem example, the first frame of reference calls the ladybugs to increase (blessing) to resolve the problem. The second frame of reference calls for the aphid population to decrease (curse) to resolve the problem. The end result, in either case, is the same, a resolution of the damage caused by aphids.
Some people are most comfortable working from a strictly 'positive' frame of reference. These people could be called 'lightworkers'*. Their primary form of magic is that of blessings. Other people are more comfortable working from a strictly 'negative' frame of reference. These people describe themselves as 'dark' magic practitioners. Then there is the group that uses a blended approach, like myself, who could be described as 'gray' magic practitioners.
The frame of reference is not always an accurate reflection of the intention of the person's actions. As such, it is possible that a person who is working a blessing has a targeted goal that will cause harm or distress to another individual. This is where one must take careful stock of what it is they are attempting to achieve. Blessing and cursing are mere mechanisms of how it manifests.
* 'Lightworker' is a popular term for people who do primarily positive (increasing) magic. Some people assume that the differences between light, dark, and gray magic are divisions between good and evil. I would invite those who make this assumption to review the previous discussion of the problem of evil on this blog here.