Yes, Sanders supporters know that he's talked about raising taxes.
The problem is that it's always raising taxes on 'other people' so that doesn't bother his supporters. It's the Occupy Wall Street thing all over again - let's just tax the shit out of the top 1% in order to pay for free shit for the 99%. Except that if you taxed the top 1% at a rate of 100%, that still only gets you 4 months of the federal budget. Then the 99% either still has to pony up, or the wheels come off the global economy.
In reality, in order for Sanders to do even half of what he's talking about, he would need to substantially raise taxes on everybody, even after closing all the loopholes that everyone loves to talk about. In reality, we need to raise taxes *right now* in order to pay for all the shit we're currently spending money on, or stop spending all that money. It's basic math, and Congress gets an F in basic math every year.