The phrase "defensible reason" means having a logical and justifiable explanation or justification for a belief, action, or decision. It implies that the reason can be backed up with valid evidence or arguments. Full definition
There are few defensible reasons for supply management to exist. (canadianbusiness.com)
Because the park's display includes a Hanukkah toy, the dreidel, Finnegan's complaint noted «no legally defensible reason» for the exclusion of the Nativity scene. (articles.chicagotribune.com)
In short, the only defensible reason for «conservative» economists to discuss carbon taxes is as a TOTAL replacement for ALL EPA greenhouse gas regulations. (globalwarming.org)