Facts do not care about your feelings, Ms. Warren. Like it or not (and, like most on the left, I most assuredly do not), Fox News is the No. 1 most-watched news channel in the USA.
Only a fool too incompetent to campaign properly would turn down a chance to market her platform to an audience that size. Especially when you consider the not-insignificant number of voters who voted for Obama twice (and/or for Sanders once in the primary), and decided to either sit the 2016 general election out or vote for Trump. There are, in short, persuadable viewers on Fox News; Ms. Warren decided to write them off.
This is not a center versus left thing, either. Both Sanders and Buttigieg got it, and decided to accept Fox News’ invitations despite their personal dislikes of that network’s overall politics.
It is also not purely campaign realpolitik. If Warren’s gut reactions get the best of her when it comes to Trump’s trolling or Fox News’ editorial record, odds are gut reactions will get the best of her as president when she has to quickly respond to crises. That’s the last thing we need.