Responses are optional... It is your choice to trigger them or not
From pag 23 of Core rules:
Responses are denoted by a bold “Response:” trigger
on a card. Responses are always optional, and can
be triggered by their controller in response to (i.e.
immediately after) a specified game occurrence. In
order to trigger a response on a hero, ally, or attachment
card, the card on which the response is printed must
be in play, unless the response specifies that it can be
triggered from an out of play state. Event cards with
“Response:” effects are responses that are played from
a player’s hand.
The ally card Son of Arnor provides an example of
a response effect that can be triggered (at a player’s
discretion) whenever its specified trigger (“after Son of
Arnor enters play”) is met