once we're on the topic of ribbis

Another small question:  The gemara records a machlokes between r yochanan and r elazar as to whether ribbis, once given, is forcibly taken by beis din to be returned to the borrower.  Why does R Yochanan think that once the malveh takes the ribbis, we let him keep it?  The gemara explains:  מות יומת דמיו בו יהיה - הוקשו מלוי רבית לשופכי דמים, מה שופכי דמים לא ניתנו להשבון - אף מלוי רבית לא נתנו להשבון - the torah compares malvei ribbis to murderers - just like a murderer cannot atone by undoing his actions (because his actions cannot be undone), so too malvei ribbis cannot atone by giving back the ribbis.

The problem is, gazlanim are also compared to shofchei damim - and there we clearly allow for (and mandate) the returning of stolen goods.  כל הגוזל את חבירו שוה פרוטה כאילו נוטל נשמתו ממנו שנ'  כן ארחות כל בוצע בצע את נפש בעליו יקח (rambam, gezeilah 1:13 based on BK somewhere) - doesnt this prove that the fact that the pasuk compares an issur to murder doesnt mean that the issur cannot be undone?