

Left and right started as arbitrary concept based on where political parties sit in a parliament and they totally depend on the circumstances of the political system. In European history at the time democracies came into existence you could have separated idiological streams into e.g. republicans (as in people who aim for a republic) and monarchists. Also the more political parties with different topics there are the more difficult it gets to assign them to either left or right. As another commenter stated… dividing a political system into left and right helps to define a common „enemy“ which moves away the political discourse from other topics that matter.
TL;DR: Mandatory helmet -> less cyclists -> potentially more cars -> less safety
I guess one aspect of safety for cyclists is having less cars on the streets, but the logic of the clickbait headline is twisted.