Those making excuses in advance ("it's the weather") would have *nothing at all* to say if they held no concerns that the protest will be effective. They're angry - that's a good sign.
Many (not all!) older folks will *always* moan about younger folks. As someone from an older generation, I'd say that the reasons are sadly obvious. They'd *love* this to be a clear example of young vs old, whereas reality is nothing of the sort.