Without https, a man in the middle could easily rewrite your website's content in different ways for different purposes, inject scripts, etc. Which at first sounds a little theoretical except that ISPs have actually done this to inject banner ads into unsecured pages (article's about a smaller ISP, but iirc Comcast has done this before as well): https://arstechnica.com/tech-policy/2013/04/how-a-banner-ad-...