Is it true that most employers in the USA look down on an online degree holder?

I certainly haven't seen statistics that support this claim, but it's probably true that at least half of people who routinely hire recent college graduates prefer those who attended brick-and-mortar institutions for traditional campus degree programs over those who earned their degrees online. There are multiple reasons why I think that's the case, some good and some bad, but the why is a bit out of scope given the question. Given a choice between a brick-and -mortar university and an online degree program, it's generally better to be in a brick-and-mortar, f2f program.

This is just one data point, but Jeff Erickson has attested that computer science master's degree students attending UIUC in person have asked for letters attesting that they earned their degree on campus, rather than in the ostensibly equal online program.

However, if you need to attend online, it's better to have a degree than not (assuming you want to work as a white collar professional in the United States). It's also generally better to choose an online program from a brick-and-mortar institution than an online-only or primarily online institution. Online aren't worthless. While I am not personally involved with my departments online degree program, I've met some of the students and graduates and many are quite successful.