Adjective
(of a person) Not giving reflection or thought to one's actions, words, conclusions, etc.; (of an action, statement, conclusion, etc.) done without reflection or thought.
Synonym: impulsive
That does not reflect light or sound.
Source: en.wiktionary.orgThat a majority of women do not wish for any important change in their social and civil condition, merely proves that they are the unreflecting slaves of custom. Lydia Maria Child
And yet not choice but habit rules the unreflecting herd. William Wordsworth