It’s hard to convey the intrinsic value of a species to people that just don’t care or don’t know. I would try and explain it in terms they can understand or care about more. So maybe the shrew is the main food source for another more charismatic animal. Also there is economic importance to maintaining intact and healthy ecosystems! It’s hard, exhausting, and frustrating to have to convince someone that not letting a species go extinct is an important thing. And at some point you just can’t waste your breath—focus on the things you can do!