It's a weird thing to say, but punching someone, is just one act against one person.
But littering is one act against a community. With zero regard for the safety and well being of children, the elderly, the infirm - or your own society. It's an impersonal crime and in terms of a community one of the worst things you can do.
And while I am not a fan of draconian punishments, people manage not to litter for very long in Singapore ...
I am aware I may be an outlier on this.