Plagiarism is serious business. Using someone else's words, without giving the original speaker credit for them, is simply wrong. It should not be done, and if it is, is should be punished. Melania Trump should have to face up to the charges and be penalized, in some manner, for her acts.
I am definitely of the opinion that Melania Trump, or at least those people who make up her publicity team, should face penalties for plagiarising one of Michelle Obama's speeches. If nothing else, she and her husband should lose credibility when her words are so obviously and transparently not her own.
Melania Trump should not be penalized for plagiarizing Michelle Obama's speech unless Obama decides to pursue legal action. I doubt Michelle Obama is petty enough to put Melania Trump through a court of law, and will instead rely on the court of public opinion to serve justice. Besides, it was likely Trump's speech writers and not Trump herself who did the plagiarizing.
Melania Trump's speech was almost certainly plagiarized. This is very unethical and makes the Trump campaign look even more awful than it already did. However, there should not be a penalty. We have freedom of speech in this country, and it would be wrong to penalize her. The penalty, ideally, will be people recognizing how unethical and dishonest the Trump campaign is, and deciding not to vote for him in November.