The opposites of “rigid” are more unflattering than rigidity:
lenient indulgent broken compromising easy imprecise indefinite inexact irresolute unfixed unreliable accommodating liberal permissive resigned soft-hearted
And that’s the problem with name-calling. When we impose a derogatory label on someone, we invite scrutiny upon ourselves. We label ourselves as the opposite of the names we impose on others.
Some of us are better at name-calling than others. Donald Trump does a lot of labeling.