Q:

Why is a comma a bad record separator/delimiter in CSV files?

I was reading this article and I'm curious for the proper answer to this question. 
The only thing that comes to my mind it's perhaps that in some countries the decimal separator is a comma, and it may be problems when sharing data in CSV, but I'm not really sure of my answer.

A:

CSV format specification is defined in RFC 4180. This specification was published because 

there is no formal specification in existence, which allows for a wide
  variety of interpretations of CSV files

Unfortunately, since 2005 (date of publishing the RFC), nothing has changed. We still have a wide variety of implementations. The general approach defined in RFC 4180 is to enclose fields containing characters such as commas in quotation marks, this recommendation however is not always meet by different software.
The problem is that in various European locales comma character serves as the decimal point, so you write 0,005 instead of 0.005. Yet in other cases, commas are used instead of spaces to signal digit groups, e.g. 4,000,000.00 (see here). In both cases using commas would possibly lead to errors in reading data from csv files because your software does not really know if 0,005, 0,1 are two numbers or four different numbers (see example here).
Last but not least, if you store text in your data file, then commas are much more common in text than, for example, semicolons, so if your text is not enclosed in quotation marks, that such data can also be easily read with errors.
Nothing makes commas better, or worse field separators as far as CSV files are used in accordance with recommendations as RFC 4180 that guard from the problems described above. However if there is a risk of using the simplified CSV format that does not enclose fields in quotation marks, or the recommendation could be used inconsistently, then other separators (e.g. semicolon) seem to be safer approach.

A:

Technically comma is as good as any other character to be used as a separator. The name of the format directly refers that values are comma separated (Comma-Separated Values).
The description of CSV format is using comma as an separator.
Any field containing comma should be double-quoted. So that does not cause a problem for reading data in. See the point 6 from the description:

Fields containing line breaks (CRLF), double quotes, and commas
     should be enclosed in double-quotes.

For example the functions read.csv and write.csv from R by default are using comma as a separator.

A:

In addition to being a digit separator in numbers, it is also forms part of address (such as customer address etc) in many countries. While some countries have short well-define addresses, many others have, long-winding addresses including, sometimes two commas in the same line. Good CSV files enclose all such data in double quotes. But over-simplistic, poorly written parsers don't provide for reading and differentiating such. (Then, there is the problem of using double quotes as part of the data, such as quote from a poem). 

