To be fair California (and all the other states) don't trust their citizens to pay the use tax with good reason - the vast, vast majority don't. Not only is it complicated and time consuming for the individual consumer to do so it also results in things online costing more than they appear to and thus less money in their pocket.
Amazon also trusts the citizens aren't going to pay the use tax - their entire business model requires it and thus why they are fighting so hard against it. Without being able to avoid paying taxes the goods Amazon (and other online retailers) sell aren't particularly better priced than those you could buy at your local brick and mortar store - so instead of the purchase tradeoff being something like 20% cheaper on Amazon but more convenient at a local store it would become only a 5-10% price advantage at which point they start losing a lot of sales due to convenience. I'm sure brick and mortar stores would love to be able to use Amazons 'the customer is responsible for paying the sales tax' line and drop all their prices too. However we don't do that for two major reasons (1) It is completely rediculous and wasteful to force the customer to track and record all their purchases and once annually pay the accumulated tax amount rather than having the retailer collect it at the time of purchase with minimal cost or imposition and (2) People won't pay it and the cost of tracking purchases down and litigating non-payment would be prohibitive, just like doing it for online purchases is.
Amazon can not be nearly as profitable if they had to charge customers the real cost of items so their business model relies on encouraging widescale fraud in order to maintain a price disparity. It is unethical and immoral and probably illegal too. If it isn't actually illegal than it should be - something that these laws intend to address.