You raise multiple questions, all very important and interesting, which intersect in various ways, but which, I think, can be distinguished. (1) Are reasons causes? (2) Is an agent constrained if s/he acts for reasons? (3) Can one freely act against one's own better judgment? (4) Even if one could freely act against one's own better judgment, would the ability to do so be valuable in the way that freedom is valuable? (Now (4) gives rise to a further question: In what respect is freedom valuable?)
Now it seems to me that the question that's driving you here is whether agents can be determined--"governed"--by reasons and nevertheless free, and so I'll treat it. (Note that I've subtly shifted the question from whether agents can act for reasons and still be free to whether agents determined by reasons can still be free. I do so in order to focus the question on choice, which I take to be the locus of freedom, and away from action, which requires a different sort of analysis.)
In order to answer this question, however, it would first need to be determined to what sort of determination a free agent can be subject and remain free. (Certain philosophers would accept that reasons can be deterministic causes of actions or choices, whereas other philosophers would not.) It seems to me that the vise tightens if one assumes, for the sake of argument, that reasons determine an agent just as physical causes determine effects, so I proceed from that assumption.
Now, suppose that reasons determine an agent. The worry is that then the agent is not free, because s/he is determined. But as both philosophers--such as Locke and Leibniz, to take two very different kinds of philosophers--and novelists (Dostoyevsky, in Notes from Underground) have argued or suggested that the freedom to be irrational isn't even worth the name of freedom. Indeed, Leibniz even claims that freedom varies directly with rationality. (He's got theological reasons for making this claim, but let's leave those aside.) Now Leibniz--and I'm inclined to agree with Leibniz on this--thinks that determination by reasons isn't any sort of constraint or compulsion, but a perfection, and so determination by reasons shouldn't be seen as a limitation or constraint--that's the wrong way to conceive of one's relation to reasons. Indeed, it seems to me that in order even to be capable of being an agent, one must be capable of acting for reasons; consequently, it would therefore seem to me to follow that determination by reasons does not--indeed, cannot--compromise freedom.
Now if one has a different conception of agency than the one just sketched, one might want to resist the idea that agency and determination by reasons are compatible. But what underwrites such a conception of agency? Why should one want a conception of agency that sees rational determination as a threat? This takes us back to question (5) above: What's valuable about agency? That is a question to which I wish I had an answer.