Can you just refuse to discuss a topic at all ? I mean... is that legal ?
Like the original comment said, the purpose of a body like the congress is to "...debate an issue, vote on it, and then to enact the result of the vote..." At least, I thought that was how things worked. Is it the case that congress doesn't even consider debating certain issues ?
It is legal yes. Each house of Congress gets to decide their own rules (by law), in the House of Representatives that is done by and through the Rules Committee.
Initially it would just propose general rules at the start of the session then dissolve, but in the late 19th some realised it could propose bill-specific "special rules" (requiring a simple majority vote) giving it significantly more power and control over House proceeedings, and that's basically what it has been since.
As a result, by controlling the Rules Committee the majority can decide which bills get to the floor (and when) regardless of their order on the Calendar of the House, can decide whether the bills can or can not be amended and can decide how much debate time will be available and who gets to talk.