Sacrificing Soul Snare is part of the cost to activate the ability. Once you activate the ability, no player can do anything to Soul Snare to stop you from activating it.
18-06-2021
wotc
If Soul Snare's ability targets a creature that's attacking a planeswalker you control, but that planeswalker is no longer on the battlefield as the ability tries to resolve, the attacking creature will be an illegal target and Soul Snare's ability won't exile that creature.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.