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Shield counters don't prevent players from sacrificing creatures.

“Shield” is not an ability that creatures have and shield counters are not keyword counters. If a creature with a shield counter loses its abilities, the shield counter will still protect it as normal.

A creature with a shield counter on it may still be destroyed by state-based actions if it has damage marked on it equal to its toughness or has been dealt unpreventable damage by a source with deathtouch.

If a permanent that would be dealt damage has more than one shield counter on it, that damage is prevented and only one shield counter is removed.

If a permanent with a shield counter is dealt unpreventable damage, that damage will be dealt and a shield counter will still be removed.

If the attacking creature loses its last shield counter at the same time it deals combat damage to a player (for example, if the attacking creature has trample and would be dealt damage by a blocker), then you will not be able to pay the cost of removing a counter when the triggered ability resolves.

Neither the triggered ability that puts a shield counter on a target attacking creature nor the triggered ability that removes a shield counter from it are optional.

Removing a shield counter in this way isn't the same as regenerating a creature.