While this particular incident is the action of the one nutter, 63m people voted for Trump despite his anti Muslim, anti Mexican, etc. rethoric & his alt-right team. So I'd have questions about what the opinion of the entire country actually is. If I were a person of colour/muslin faith I'd be even more reluctant.
I agree with your opinion. Why visit a country that elected a President that completely opposes immigrants coming into his country? USA's President has made it very clear that the country doesn't want any immigrants. I know that he's facing a lot of backlash and most people here would say that they're not with the same view as Trump, but guess what? Trump calls the shots for at least the next 4 years. It is extremely saddening, but the United States government is officially showing immigrants the finger.
I don't feel it is valid because it is rather nonsensical to group an entire country of 300 plus million into the same teaspoon of, at most, a handful of mentally insane killers.
It's not about saying everyone or even most people in the US are racist. It's about considering whether a visit would be marred by the current miasma of (institutional?) racism/anti-immigrant sentiment.
For example: would you, as a US citizen, choose to visit Iran vs going somewhere else?
Why bother risking personal harm to visit a country that expressly doesn't seem to want you?
Edit: Would down-voters like to comment on why this isn't a valid stance?