The word "karma" is widely and wildly misunderstood and used wrong so of course it is nonsense.
Karma means action (not the results of action).
Action is real. Karma is action, thus who will deny the reality of karma?
Now onto the results of actions, that which we seek searching to satisfy of our desires.
The accurate word here is "karma-phala" (fruits of actions).
Who will desire that actions bring results?
If it were otherwise, we would not act. If the results of actions were entirely random, we would cease acting in expectation of particular satisfactions. We act because karma-phala is generally consistent with our desired results. But, there is many a slip between cup and lip.
Results are not always completely foreseen nor wanted. Desire is like blinders on wisdom.
Bad and stupid choices, actions, usually bring poor results, shitty lives here and now. Actions habitually taken that manifest better results smooth our way in this life.
That is the meaning of karma, taken as a philosophy that is self sustaining without reincarnation.
I am one of those who live life knowing that karmic-results of karmic-actions are as certain as gravity.
Of course, there exist folk who insist that gravity is not real.
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