A goer is something viable, or someone active. A goner is something inviable, or someone who is going nowhere because they're about to die. | An owner is someone to whom a thing belongs. An ower is someone to whom it doesn't belong, who has to give it back. | A diner eats while a dinner is eaten. | If you don't mind rather antiquated English and also don't mind contractions, I bet I can find "Do't!" (do it) in Shakespeare (... I checked, and yes I can), and of course "don't!" would be an excellent way to contradict that instruction. | If something is unpraised then it will not be upraised (at least not in the sense of "exalted"). | Oh, and here's an unequivocal pair of opposites: aesthesia (the capacity to sense things) and anesthesia (what you get when that is taken away).
For #2, a pile of not-really-opposites (but I don't find the "official" answer very convincing either, I'm afraid):
Not exactly opposites, but I like the fact that we have Bern and Berlin. An alkane is never alkaline but these aren't opposites either. If you're in a fight then your opponent's deadliness corresponds to your own likely deadness, but that's some way from a real pair of opposites. I suppose acyclic and alicyclic are almost opposites, but "alicyclic" = "not acyclic AND ALSO aliphatic". A case of alliteration is one where a certain sort of alteration (change of consonant) isn't there, but again not really opposites.
(Note: I am using computer assistance, which may be disqualifying depending on @Trenin's intentions.)
The following were found when I was under the misapprehension that #2 was looking for LL rather than LI. The first is mostly a joke.
Troops are mostly men, do their work standing up, and are highly thought of in society even though they harm others for a living. Trollops, on the other hand, are mostly women, do their work lying down, and are disdained by society even though they please others for a living. | What is leveed is raised up in an embankment. What is levelled is made flat.