The way policy debate works (traditionally) is that the affirmative side gets to choose a particular policy to advocate within a broad space. A negative side that sticks to refuting the particular details of that policy is putting themselves at a severe disadvantage - they're always going to be behind in research and debate experience on that topic relative the affirmative (unless maybe they happen to use that same policy proposal themselves when assigned the affirmative). So debaters have used generic negative strategies for many decades, not just meta-critiques of their opponents discursive approach or assumptions ("Ks") but also "disadvantages" based on generalities like "your proposal will use up political capital and prevent Y from happening", and topicality arguments, where e.g. there might be two (or more) facially plausible interpretations of what's in scope for the topic, and they'll argue that whichever the affirmative has used to justify their proposal is incorrect.
Debate is competitive. Yes, each side wants to "get one over" or "blindside" their opponent, but that's not different with the K than with any other creative argument or novel bit of research, and at higher competitive levels everyone is going to be quite comfortable debating the K (at least since the 1990s).
It is. The main advantage that the negative has is that they only need to win 1 of what are called the 5 "stock issues" in order to win a policy debate round. Furthermore, the negative can also run something called a "counter-plan," which I talked about in another comment. That's basically something structured a bit like the affirmative plan, but which (typically) does not affirm the resolution. That's frequently enough to put the affirmative off balance, because the negative has essentially free reign to argue for anything outside of the resolution.
Debate is competitive. Yes, each side wants to "get one over" or "blindside" their opponent, but that's not different with the K than with any other creative argument or novel bit of research, and at higher competitive levels everyone is going to be quite comfortable debating the K (at least since the 1990s).