In the present day, the United States has huge banking behemoths that collectively control or manage a significant amount of the assets of this great country, of which prior to the 1980s, this situation simply didn't exist; because legislation so previously passed, was done so as to limit banking institutions to their State of residency, thereof, and further that these financial institutions were not permitted to bank beyond the borders of their State of residency. The primary reason why interstate banking is a grave mistake is the fact that when that government of, by, and for the people, does not restrict banks from crossing State borders, then inevitably what occurs, is that these banks become too large and cumbersome, and do thereof accumulate many ill and non-performing investments, that subsequently get labeled as being "too big to fail," and when that ensuing financial crisis does come, what thereby occurs is that those banks end up being supported and bailed out explicitly by the taxpayer's money, so that in effect, in good times, banks profit upon the citizen's backs, and in bad times, those same citizens make good on that banking greed gone so horribly wrong.
The United States of America is the richest nation in the world, and banks were created to be a depository of the people's money, for the expressed benefit of those people in regards to prudent loans and investments being so made; but what has occurred through today's interstate banking is that a significant amount of interstate banking institutions have made it quite clear that they are beholden to just one thing, which is the making of money for that bank, above all, and the people, thereof, be damned. So too, when banks are restricted to just local communities, cities thereof, and their specific State, those banks typically make it a point to utilize their assets in conjunction with those communities, so that those monies so being deposited therein, are recycled within those communities. On the other hand, interstate banking institutions, are national in structure, signifying that some communities thereof are quite obviously going to be net losers to those monies so being earned, deposited and dispersed, whereas others will be net winners; and of which typically the result of such, is the greater overall concentration of wealth into fewer and fewer hands and institutions, thereby making a very few being benefited and wealthier, at the expense of the many who are the losers, and thereby poorer.
In a country in which some of the States thereof, are so productive and wealthy, that if they were classified as a separate country, they would rank as high as fifth in the world, in terms of the size of its respective economy, has no ready need to expand its banking beyond the borders of that State. It is proper to recognize that this country is a voluntary union of States, of which, each State has its own separate Constitution, for the express purpose to benefit those State residents; and therefore it so follows that regulated State banking institutions will therefore, more times than not, do what is best for those State residents; whereas national banking institutions, will, as a matter of course, do what is best for their bottom line, foremost, and care not a whit about anything else.