Do you think some things should never be brought up unless they actually happen (molestation)?

My MIL sent my SIL a text about child molesters and how she needs to be watching her boyfriend around her kids. My MIL was telling me and my husband that she just meant my SIL needs to be more careful about who she leaves her kids with because she will leave her kids with anybody, 12 and 11 year old boys, 6 year and two 3 year old girls. My SIL was telling me and my husband "why even bring up something like that? why bring it up unless it happens? you shouldn't even talk about stuff like that....." They both talked to us on separate occasions. I do not think for one minute this man she has been seeing off and on for years is a child molester but I also think my SIL SHOULD be more careful (being a victim herself). I don't think child molestation should be a forbidden topic. It happens, don't ignore it, deal with it. If your mother has a true concern for your kids why should you be mad at her? What do you think? Should things like this be swept under the rug unless it happens to you or your kids?