I totally agree that it can be done by starting with freerolls. I don't think freerolls, themselves, will teach you how to play well. People don't play well and you can do some really bad stuff and still do fine in the freerolls. But, they are a way to get real money to sit in the real games and start practicing for real. You can also play well in freerolls, you should actually, and learn a little. You just won't become a great player if you've only played in freerolls. You'll have to move out of them eventually.
Personally, I have only deposited on one site. And that was a $50 deposit just because you needed a certain amount of points from real money play to get into a really +EV freeroll (which I won $700 in and promptly withdrew my original $50 deposit). The rest of the sites, I have built my bankroll from freerolls. So, I can also state that it can be done.
Now, as I get older, I am getting more and more inclined to just deposit money and start out with a full bankroll. It also would allow me to take advantage of first deposit bonuses and other stuff like that, which build bankrolls faster. It just takes so long to grind up from freerolls.
I am playing on ACR, for example, grinding up from their freerolls. I cashed in a couple, got a couple dollars, and started playing the cash games. I'm playing PLO2 (which is extremely swingy and a bad choice when you are under-rolled like this). I've been up to $9, and I am back down now to $2.50 after a typical amount of variance. There's a good chance that I will lose it all and be back to the freerolls to get more.
If I think back, most of the sites I have money on, or had money on before withdrawing, started in a similar way. Days or weeks of freeroll grinding following by weeks or months bobbing around just above $0 until I had enough to play full stacked with a bankroll. Then slowly grinding my way up. It can be done, and it's great for learning. Even if you deposit, I recommend starting at the micros and making sure you can beat them first. They're not hard to beat, and you beat them by having a strong foundation