Of cource you are right about the social context. Elizabeth shouldn't be encouraged for such a marriage. Darcy thought of that: "He wisely resolved to be particularly careful that no sign of admiration should now escape him, nothing that could elevate her with the hope of influencing his felicity;"(ch 12) As you put it he "did not want to lead Elizabeth on".

But at first his concern was mostly for himself: "...he should be in some danger." (ch 10) And it was him who was led on before he could realize it. "She attracted him more than he liked." (ch 12)
He was a clever man and surely he thought all these about E's reputation etc. But IMO he firstly thought of himself. His concern for E was only a result of his growing feelings for her.
And until now, he is the only victim of this hopeless situation.