MickTheCyclist wrote: ... After much thought they cancelled the self-organised idea and decided to participate in a local sportive instead. ...
I think this bit is the key - why did they take this line?
All sorts of possibilities but one is that they wanted to avoid the risks of DIY - leave it to somebody with more experience. I get the impression you have already decided to sit this one out. As this is work-related and you are probably known within the company as a committed cyclist, it may lead to questions being asked about lack of loyalty in not supporting the event. Only you know whether your principles are worth risking upsetting your employer. One thing is for sure: you are not going to convince them that wearing helmets is a bad thing, but you may convince them you are a loony if you try.
That isn't based on ethics but rather the practicalities. Hopefully common sense advice on an issue governed by "common sense."