Hmm from what I've read it's not actually that.
Put in rather simple terms there but it does make sense.
From all the interwebs reading I've done so far it looks like, unless you are running massive boost, the turbo will be fine. The issues seem to be: Metering the air a second time as it goes back past the MAF on the way out which causes overfuelling, thus backfire and dead cats. Personally I think it'll put unwanted strain on your throttle body, but I've seen zero people saying it's an issue so far. Also if you have any oil in your intake pipes, that's going to be spat back into the MAF which can't end too well for it, I guess the air filter too.