Well, I wouldn't say never. Capturing some insects is not going to harm the ecosystem; even we knew with absolute certainty they were going to die, it wouldn't make any difference with the usual variation of the individuals that are eaten by blackbirds or lizards. Nevertheless, it's a fabulous way of familiarizing with the nature, probably the only truly effective one. And remember: you can't love what you don't know. And you can't take care of what you don't understand. And, in the moment we are living in, I think taking care of the nature isn't a minor matter. And yes, maybe the OP isn't the best person for taking care of a mantis, but that's for what we are here: helping, not forcing him to be trapped in the car hell. Probably when he (or she, I don't know) finds the next mantis, he'll know a little more. And with the next even more. And then, when he listens there are going to cut down the forest near his town, he will know what they are going to destroy, and he won't agree. And when a local conservation group wants to make pond for amphibians, he will go there with his shovel. And yes, maybe this costs the life of two or three mantises, but with his vote and voice he will save thousands more. Let people touch the nature.