Couch surfing at a stranger's home is like staying at a hostle or homeless shelter and is very risky to you and your belongings. On the other side of that, letting a complete stranger into your home to sleep on your couch is also risky and could get you robbed, hurt, and/or killed.
Couchsurfing (with a modicum of due caution) isn't staying with or hosting "complete strangers". You can check previous references left by other guests/hosts that the person has had. Plus, well-functioning hospitality exchange platforms tend to have an active userbase small enough that everyone kind of knows each other. I've hosted a number of people with whom I've turned out to have mutual friends.
People have been "robbed and hurt" on Couchsurfing, but beyond the rare petty theft that could even happen when hosting friends (yes, people's friends can steal too) or relatives (many people have a klepto in the family), violent incidents are rare and the cases I am aware of were single females unwisely hosting single males. I am unaware of anyone ever being killed. Maybe you would like to back up your assertion somehow?
Couchsurfing is nothing new. It superseded its website forebear Hospitality Club, which in turn inherited, among other things, mailing lists for hospitality exchange among hitchhikers and nomadic travellers. There's also WarmShowers, a community for cycle tourists, that has been around for years now and goes back to a pre-internet paper directory. With years of experience and millions of host-guest interactions, you cannot reasonably claim that hospitality exchange is more dangerous than, say, driving one's car on a daily basis.