In the case of , the Runner is the one trashing the host ice, so s/he suffers damage from . When the Corporation trashes a card from the top of R&D from 's ability or trashes a piece of ice from the Runner playing a , then the Corporation is the one trashing the card and Hostile Infrastructure does not trigger.
I am curious about which of these scenarios would be considered the Runner trashing a card:
The Runner has installed a Parasite onto a piece of ice, and the ice is eventually reduced to 0 strength, resulting in Parasite's effect trashing it.
The Runner ID of choice is Noise ("Whenever you install a virus program, the Corp trashes the top card of R&D"). The Runner plays a virus, causing the top card of R&D to be trashed.
The Runner plays Forged Activation Orders on an ice that the Corp could legally rez, but the Corp player declines to rez it, trashing it instead.
The Runner plays Forged Activation Orders on an ice that the Corp cannot legally rez, thus forcing the Corp to elect to trash it.
If a card effect does not specify which player is trashing the card, then whoever owns the card with the effect is responsible for the trashing. If that player is the Runner, then Hostile Infrastructure triggers.