Repeating the question from the title

Question. How does one call an argument where premises do not necessarily lead to a conclusion?

By "not necessarily lead to a conclusion", I mean that given the premises are true, the conclusion may or may not be true (i.e., further justification is required). To make things concrete, let's consider following simple argument as an example:

Argument. Some prostitutes are being treated very badly. Therefore, prostitution should be banned.

The argument doesn't seem to be invalid (at least I don't see what "counterexample" one can come up with to invalidate it), but at the same time I don't see how the argument is valid. It is clear that the issue surrounding prostitution is complicated, and there is definitely some contention about whether prostitution should be legalized. And so it seems to me that "some prostitutes are being treated very badly" is simply not a sufficient evidence to justify the ban of the prostitution.

So coming back to the question: how does one call an argument where it is possible that the conclusion is true, but the premises listed are not sufficient to prove it?