YANBU!!!! At least, that's the way I feel, but my the rational part of me kind of disagrees.
Like you, I truly hate motorbikes... I have seen (and will never forget seeing) a number of very nasty accidents, some involving fatalities. I woud hate for anybody I love to ride one.
However ... you will probably have to accept that this is what your DH wants to do, and that it is his decision. Most bikers stay safe and do not have accidents, most are sensible on the roads, most keep a wary eye out for nutty car drivers.
If your DH is going to do this at all, then it is fair enough that he does it on Father's Day, because it is something he wants to do.
In your position, I would feel exactly the same, but I think we probably both have to learn to let our menfolk do whatever they want to do, however scary it is. We would perhaps be fairly annoyed if they tried to stop us from doing various things that they felt were inappropriate for us as mothers.
(and, to put this in perspective, I spoke the other day to a mum of two boys whose husband is currently in Syria volunteering to drive a lorry full of first aid equipment etc. - she respects his decision to go there but obviously wishes he wasn't there, and is worried sick about him... riding a motorbike as a leisure activity pales into insignificance beside choosing to take that kind of risk!!!)