You can still give all the neg rep you want. Now, you just have to have the BALLS to put your name behind your negative rep. and can't do it anonymously. Have the stones to stand behind your criticism, not hide behind an anonymous button. If you feel compelled to pass neg rep, man up and give a reason. What's the point if the person doesn't know why you disagree?
Entirely 2 different things. Sometimes a disagreement of opinion or bad info doesn't necessarily warrant an actual negative rep.
Unhelpful rating is more for public viewing to sort thru troll posts, bad attitudes and and bad info with one quick glance.
Neg reps are stupid because people often take them far too seriously then you get a PM wanting to "talk about it". They are also not publicly viewable and do nothing to deter bad info.
Unhelpful post rating can just show public distaste in a post and not have to go as far to drag it out into some big thing it was never intended to be.
In this instance I would give your post an unhelpful rating but because this forum is only one sided, you have 6 helpful ratings when in reality the majority of people may not agree with you.