You do realise that skateboarding on benches means people are slamming metal against the thing with a, probably, 40-80 kilo human being on top of it? It is really damaging.
I used to skate myself and I am not against it, but it is definitely damaging.
You could argue that public property should be usable by the public in any legal way as they see fit; however, city ordnances often do prohibit sleeping in public places, so using a bench for sleeping is not a permitted use no matter how it's designed.
There's also a big confusion in the discussion with "ordinance" vs "zoning"
There are parks near my house you can sleep/camp in, and others you can't. There are parks you can skate in, complete with some cool government built and maintained structures, and there are parks you can't skate in.
Zoning differs in every municipality in the world but locally there's zoning codes for neighborhood park, resort/campground park, and formal gardens type park.
Arguing some homeless dude has to be supported to sleep and live in a neighborhood park is exactly like demanding I should be able to build a leather tannery or chromium plating operation in my backyard, because I want to and who cares who it bothers.
> Arguing some homeless dude has to be supported to sleep and live in a neighborhood park
"Some homeless dude" would in my case be my own sister if my country were as anti-social as some other countries.
If "we make structures to keep homeless out of sight of the 'normal populace'" applies to your country, then your country is already in the moral wrong for not supporting your homeless by providing them with dignified housing.
There is no excuse you can make for compounding on that that won't make it even more morally wrong.