Mere assertions remain gratuitous until supported by arguments. Quod gratis asseritur, gratis negatur. That which is gratuitously assertible is gratuitously deniable. Thus one is right to demand arguments from those who make assertions. It is worth pointing out, however, that the difference between making an assertion and giving an argument is not absolute. Since no argument can prove its own premises, they must remain mere assertions from within the context of the argument. No doubt they too can be supported by further arguments, but eventually one comes to ultimate premises that can only be asserted, not argued.
Argument cannot free us of assertion since every argument has premises and they must be asserted if one is making an argument as opposed to merely entertaining one. One who makes an argument is not merely asserting its conclusion; he is asserting its conclusion on the basis of premises that function as reasons for the assertion; and yet the premises themselves are merely asserted. There is no escaping the need to make assertions.
If you refuse to accept ultimate premisses, then you are bound for a vicious infinite regress or a vicious circle, between which there is nothing to choose. (The viciousness of a logical circle is not mitigated by increasing its 'diameter.') This shows the limited value of argument and discursive rationality. One cannot avoid the immediate taking of something for true. For example, I immediately take it to be true, on the basis of sense perception, that a couple of black cats are lounging on my desk: