The first quote you made is from a very low-quality politics forum (GagaDaily). It looks like an ignorant misuse of "infamous". You can't use that word in a "good" way. To use "infamous", about something well-known, is to say that it is a bad thing. It means "wicked, disgraceful, evil, despicable, very wrong" etc. There is no other meaning. To use the word to mean simply "well-known" or "controversial" is an error. To call MLK's well-known speech "infamous" is to make an extremely racist and bigoted utterance. Or possibly just being ignorant. What could be called infamous is Pence's use of the speech to further the ultra-right agenda. Many people think that what Steve King said in July 2016 really was infamous.
famous for something considered bad:
The list included the infamous George Drake, a double murderer.
infamous for his bigoted sense of humour.
Infamous (Cambridge Dictionary)