https://www.ijidonline.com/article/S1201-9712(19)30354-6/pdf
This is all well understood, and studied in considerable depth.
The media overreaction is typical, but here at HN we are better than that and we should strive to rely on established science (where available). No need to throw out extreme or unreasonable numbers!
Colds are quite different to flues.
I used influenza because it was convenient in terms of available research, I could grab in a minute or two, but I'm sure if you care to look you can find similar data for rhinovirus.
Rhinovirus and influenza have very comparable R0's. R0 is the epidemiological measure of the "contagion" factor of a pathogen.
We could try to make the comparison you are suggesting instead. But to make a valid comparison we need to consider:
Is influenza infectious for 10 days before any symptoms show?
How many people get the influenza vaccine each year? I.e. is there some herd immunity built up?
The symptoms of influenza are universally nasty for everyone infected. No one with the flu is walking around and going to work (if you think do then you don't have the influenza virus you have a cold). It seems that at least some people with this new corona virus just have cold like symptoms and therefore will not by default be self-isolating like people with influenza naturally do.
Influenza is a useful proxy for the cold, because we have plenty of data on influenza strains with R0 very close to the cold.
Perhaps the most contagious disease we've ever encountered, the measles, has an R0 around 18. Before the 1960's, when the vaccine was licensed, we saw incidence rates as high as the .8% range yearly for measles. That is 20x more than influenza, but still orders of magnitude short of the 50% number you threw out there.
The cold and influenza both range from R0=1.3, to perhaps 6 on the very high end of estimates. 50% just isn't reasonable by any measure.
As for comparisons to this nCoV, it's still very early days and there are many unknowns. Still, there is no evidence to support an R0 even remotely close to the measles. 50% simply isn't plausible or reasonable, based on everything we know about viruses and epidemics.