No, they do not have to accept them at all. They can legally require payment in any form they choose; and they can deny acceptance of payment in any form they choose. Even the IRS has refused to accept payment for taxes in rolled coins.
No, collectors also buy rolls and bags of business strikes direct from the mint hoping to find some of high grade. They sort out the best, and spend the rest. That is how those get into circulation as well.
I spend my crap half dollars all the time. Especially those I order from the US Mint since, even though I paid a premium to look, it's cheaper to spend them than sell them once you add up all the fee's involved. I'd have to sell each one at .94 cent to break even or sell them at $1.36 to completely recover my cost. Given the quality of most of these coins, neither scenarion is likely to happen.