Yes, they can harm your plants. Mostly, they'll just make the leaves look eaten and ratty, but won't kill the plants outright.
You can knock them off your plants into a pan of soapy water. You can also spray the plants they like with insecticidal soap with NEEM oil in it. It won't kill them, but they don't seem to like it, and will move on rather than stay and feed on plants that are sprayed.
You could also place bait bags far from your desired plants. Though there is some discussion whether those don't actually attract even MORE beetles into your yard than would be there anyway.
