taking too much for granted; presumptuous.
Origin of assuming
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
expecting too much; presumptuous; arrogant
(often foll by that) if it is assumed or taken for granted (that)even assuming he understands the problem, he will never take any action
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012