People despise the homeless because they assume they are mentally ill or drug addicts, which - while unfair - is usually based on their own experiences and will be difficult to combat.

If you've never had a crazy homeless dude harass you or you've never come across the "leftovers" of a night on heroin (aka: dirty needles and the most unhealthy looking faeces you've ever seen), you either don't live in an urban centre or you don't touch grass.