If you say "killing is wrong," you're making a universal statement. Had you said "killing is wrong except under such-and-such circumstances" that would be another thing. But you don't make any distinctions. There's a difference between saying you're "against killing" and saying that you're "against killing in this context for these reasons." You aren't even saying "killing is wrong in general." You're just saying "killing is wrong."

So essentially you are making the same mistake as someone who says "if you have AA you should raise." The fact you have failed to specify any conditions or qualifications indicates a very real flaw in the statement. If you suggest folding AA at some later date, you are being inconsistent with your previous position.

If you believe some wars are justified, or that killing in self-defense is justified, then you aren't "against killing." You may be "against murder," "against killing under certain circumstances," or even "mostly against killing." But you aren't just plain "against killing."

The problem with making sweeping statements is that even if they aren't intended to be categorical, they're vague enough to allow you to change your position as it suits you. "Oh, I am against killing - but that's an exception. And so is that. And that." You can dodge any argument against you by arbitrarily changing the conditions under which killing becomes "okay." Under the circumstances it's fair for an opponent to ask you to define the specific conditions under which killing is and is not allowed. And if in a discussion on the morality of killing you claim that "killing is wrong" it's fair to interpret that position as it was expressed - as absolute.