Why can't we add -ve prefix in -ve words to become +ve meaning?

People are encourage to become +ve thinker, optimistic or sanguine. So how do you encourage them? One of the way is to speak in +ve manners or meaning to them. How to speak in +ve manners? Speak using +ve words. 

However in English words, there are more -ve words as constructing -ve words is much easier. You can easily turn a +ve meaning words to a -ve meaning words by adding prefixes such as "De-", "Dis-", "Un-", "Anti-" and etc. 

eg 1. Happy x Unhappy

eg 2. Motivate x Demotivate

eg 3. Satisfy x Dissatisfy

eg 4. Social x Antisocial

Do we have words by adding such prefixes make the -ve meaning words become +ve again? 

eg ? Sad x Unsad?; Irritate x Disirritate?; Frustrate x Defrustrate?; Rebellious x Antirebellious? and etc.

(I got all the words underline in red after adding the prefixes in front, because the auto spelling correction indicate there's no such words. LOL, really no such words at all.)

So from this day onwards, start speaking in +ve manners. It's not easy and challenging. Whenever you speak in +ve manners to people, people will feel good and in return, you'll feel good as well. Good thing doesn't come by easily but definitely worth for yourself to take up the challenge. This will surely make the world a better place if everyone is trained to speak in +ve manners. :D


PS. If anyone can find a -ve words and add prefixes to become +ve meaning, Please share in comment.