Passenger carrying highway rated tires must meet rigid standards enforced by the NHTSB. I don't know exactly what the standards are but common sense suggests they're speed rated (won't fly apart at rated speed), can tolerate heat build-up, meet traction specs on dry and wet, pavement, snow, ice, mud, etc., resist blow-out from impact, and more.
ATV tires are usually cheap Chinese crap that hold air and are somewhat round. They're tested for nothing.
Our Pioneer 1000s are capable of about 62mph, Talons 70+. Many of you carry wives and children in your machines. To me it's a no-brainer. I use highway-rated tires on my P1k.