So, "safe" is kind of a relative term. I've been vaccinated, so I feel pretty much safe wherever I go on a daily basis. I am perfectly aware of the Delta variant, and that being vaccinated isn't a silver bullet. But, at some point, you either have to shut it all down OR realize that you are going to have to assume some level of risk.
I did a workout at the park this morning, and it was a circuit of different stations- 40 seconds work, 20 seconds rest- so there wasn't time to sanitize equipment between rotations. You used the same equipment, you used the same mats, as the person ahead of you. Is it ideal? No. But the options are not participate or...assume the risk that comes with doing this particular workout.
I would not feel unsafe going on a cruise right now, but I would also know, just like we did last September, when we went to WDW, that there is still a certain amount of danger involved. I also know that the kiddos, if they did catch something, would more than likely be fine. And, they have just as much a chance, if not more, catching something at school. That said....it would make me feel a lot better if there was a vaccine for children.
I think where we have landed on it, though, is that while we may personally feel safe. While we may personally feel fine assuming a small amount of risk. Even if we personally feel like the kids would more than likely be okay if it came to that. We don't want to get stuck quarantined in a stateroom. We don't want to take the chance of a massive outbreak, meaning we may miss ports of call. So...yes we feel mostly "safe" in the health-sense of the word. Not sure we are feeling safe as far as safe from potential consequences of Covid on a sailing.