Slavery in the modern world (for the most part) is illegal and highly frowned upon, as it drastically limits the rights of the individuals. However, leaving slavery behind also created a gap in productivity, a workforce that previously could be paid simply by the initial purchase and sustained with a minimum of food, water, and shelter, now requires a salary for a more decent lifestyle. So the economy required another way to produce so much in the long term (such as the slaves did), and with this we ended up with the most common form of slavery in our day (especially in the U.S. where it is almost impossible to live decently without it), debt.
The issue is not so much small debts, such as when you use a credit card to buy your groceries at the store, but rather larger debts, such as a house and car mortgage, and most of all student loans (the student loans being the most sinister for a reason that will be explained later). These are large debts that take many years for normal people to pay off (especially in a society where consumption is promoted, making it harder for the average person to budget their salary in the most efficient manner) and create a relation between the person and the bank similar to that of an indentured servant. It is even more akin to slavery when the person is allowed to only pay the interests, damning themselves to a lifetime of debt with the bank.
Although it is true that the exploitation is not the same, it does exist. Where before slavery was typically limited to a certain peoples (usually based on race) and were forced to do physical work for the direct benefit of the slave’s owner (whether that work be field work or nannying their children, such as could be seen in Ancient Rome), in this case the slavery is not restricted by population, but rather by income, and the lower the income, the worse the consequences of this debt. When you are indebted your options are limited, you need to earn enough to pay living expenses and at the very least the interests on your loan, while if you were not indebted your job options are not restricted by a necessity to pay of a large loan lingering over you.
The worst part of this slavery is not only that you are stressed and that your options are limited, but the consequences for not paying the bill. If you fail to pay the mortgage on your house they take it away from you along with everything else you have in order to pay off what you owed. However, this is not the case of student loans, which is why in the U.S. they are the most sinister of all the debts. As many U.S. university students will know, university in the U.S. is extremely expensive, the the point that in many cases people view no other option but to join the military which will pay it off for them (another exploitation that begs for its own analysis another day), a tuition that (with scholarships) can cost $20,000 a year (not including room & board, cafeteria, or textbooks) just for a four year major (the prices go up for masters, PHDs, and doctorates). This is a lot of money that the banks have invested in young people with little to no work experience in the real world and who are in a stage and environment where they will most likely spend more on their credit cards (as many do because the banks promote it, giving students a free pizza if they get a credit card with the bank). But what makes this debt the most terrifying (at least in the U.S.) is the fact that you cannot get rid of it. If you can’t pay your house mortgage they will take away your house, but they will also take away your debt, but in the case of student loans they cannot take away your education, meaning that even if you declare bankruptcy you are stuck you your student loan until you pay it off, or until you die.
These debts are tools to impoverish the middle class and keep the working class where they are while the rich (those who can pay off these debts much faster than everyone else) are able to keep more of their income and (once they have payed of their loans) maintain a much larger income while the lower classes continue their suffering and enslavement to the banks.