Almost every insect identification request I receive includes the same question: "Is this a good bug or a bad bug?" Ok, another frequent question is "How do I get rid of it (them)?" The concept that any particular species of any organism is inherently good or bad is a symptom of collective ignorance, and I am not sure that the entomological community has done much to counteract that logic.
A good deal of our opinions and beliefs have been biased by large scale agriculture, and the fear-mongering media coverage of economic pests. You also have "organic" advocates who promote "beneficial" species, which they often have for sale in their nurseries and other businesses. The common denominator in those instances is money. Millions, if not billions, of dollars are at stake in products ranging from household and garden pesticides to bug zappers to laboratory-reared lacewings and parasitic wasps. Don't you know that you can't live without any of this stuff?
Get behind the sales pitch and the reality is much more subtle and variable. Take the praying mantis, for example. Here in the U.S. you can purchase the egg cases (ootheca) of the European Mantis, Mantis religiosa, for your garden, despite the fact that in most areas of the country you already have one if not several native species already there.
Then there is the idea that mantids are beneficial predators. Mantids are completely indiscriminate hunters. They will eat bees and butterflies as often as grasshoppers and caterpillars. There are even well-documented incidents of larger species killing hummingbirds. Mantids still looking wonderful to you now?
Phytophagous (plant-eating) insects, on the other hand, simply must be pests, right? If so, then how come so many species have been imported from overseas to control noxious weeds? Most herbivorous insects are highly "host specific," meaning they feed on only a few, closely-related plants. Those plants have learned to co-exist with the insects that eat them. The plants produce their own chemical defenses, and even "talk" to other nearby plants to warn them of an impending infestation. Native plants are better able to withstand an onslaught because they are growing in suitable soil and climate. This also allows them to quickly recover from even the most intense defoliation.
You can also not equate your garden, yard, or woodlot to a massive farm, orchard, or forest. The reason there are pests at all is because we insist on growing large scale monocultures of various crops (and I would include tree farms in that). What self-respecting European Corn Borer is going to turn up its nose (antennae?) at acres and acres of its host plant? We set the table and then complain about our uninvited guests.
The real world of nature does not play favorites, and if you want a healthy planet Earth, let alone a garden, yard, or home, then you have to stop thinking of every species as "good" or "bad." You don't have to like every creature. Personally, I don't like mantids, but I do recognize their place in the grand scheme of things, and appreciate their existence for that reason alone.
I heartily encourage a public attitude that embraces all life forms, treats them with respect, and actively cultivates a sustainable human culture in which we can all coexist....SLAP! Sorry, there was this mosquito....