This is a dangerous argument—sure, if (I did say 'if'!) it's a win for the beginners, then why not expose them to it when there's no baggage dragging them back?; but, on the other hand, in that case, in exchange for short-term gains you're giving them a long-term loss of ability to communicate with others who weren't taught that way.
(Essentially the same argument can apply to innovation; it doesn't mean that innovation is bad, just that it is rarely without cost.)
> a long-term loss of ability to communicate with others who weren't taught that way.
I'm not sure that the difference between pi and tau is severe enough to cause a communication problem. Conversion is trivial and anyone familiar with one can learn to convert to the other in about ten seconds.
Existing problems with conversion from older systems into metric make a pi<->tau conversion insignificant - and even then people manage to deal with it just fine.
(Essentially the same argument can apply to innovation; it doesn't mean that innovation is bad, just that it is rarely without cost.)