expression, i-adjective
can't be let go to waste; can't be neglected
Fixed expression meaning something or someone is too valuable or important to be treated carelessly, discarded, or ignored. Often used when one feels obligated to make use of something or to respond to someone's kindness.
彼の好意を無下にはできない。
I can't just ignore his kindness.
せっかくのチャンスを無下にはできない。
I can't let this precious opportunity go to waste.
The affirmative form meaning 'to treat carelessly' or 'to waste'; 無下にはできない is its negative potential form.
From 無下 (むげ, 'unreasonable' or 'careless') + にはできない ('cannot do'). The phrase is a fixed expression meaning 'cannot treat lightly or wastefully'.