Why is the name Mekom P'tur indicative of being entirely permissible?

Question

In the introduction to Tractate Shabbat in his Commentary to the Mishnah, Rambam writes:

אבל מקום פטור מותר להוציא ממנו לכל אחת משלש הרשיות ומהן אליו וזה מותר לכתחלה ולפיכך נקרא מקום פטור

(Kafih translation)

But a mekom p'tur it is permissible to take out from it to any one of the [other] three domains, and from them to it, and this is permissible ab initio and therefore it is called "a place of exemption".

(My translation)

Here Rambam tells us that the reason for the name mekom p'tur – place of exemption – is that carrying to and from that domain is entirely permissible. However, this seems to be a puzzling reason to give the domain this name. In the area of Shabbat, the term "exempt" (patur) usually carries the implication that the perpetrator is merely exempt, but not that the act is entirely permissible:

Shabbat 3a

והאמר שמואל כל פטורי דשבת פטור אבל אסור בר מהני תלת דפטור ומותר צידת צבי וצידת נחש ומפיס מורסא

did not Samuel say: Everything [taught as] involving no liability on the Sabbath, involves [indeed] no liability, yet it is forbidden, save these three, which involve no liability and are [also] permitted: [viz.,] the capture of a deer, the capture of a snake, and the manipulation of an abscess?

(Soncino translation)

Given that the connotation of "exempt" is expressly not "entirely permissible", why would this domain be named "a place of exemption" specifically to illustrate that it is entirely permissible?

Answer 1

The context leaves no doubt to indicate complete exemption as the use of Petur is relative to a Rabbinic enactment. The source of Makom Petur is Shabbos 7b which is talking about a specifically rabbinical forbidden to carry area called a Carmelis. Anything not within the parameters of a Rabbinic Carmelis is a place of rabbinic exemption (which means the rabbis had no concerns and allowed it) as there is no rabbinic enactment of carmelis

אין כרמלית למעלה מי' ואקילו בה רבנן מקולי רה"י ומקולי רה"ר מקולי רה"י דאי איכא מקום ארבעה הוא דהויא כרמלית ואי לא מקום פטור בעלמא הוא מקולי רה"ר דעד י' טפחים הוא דהויא כרמלי' למעלה מי' טפחים לא הויא כרמלי'

Shmuel (Shabbos 3a) is talking about non-indicative uses of Patur when refering to Petur as still being forbidden. He does not deny the word means "exempt" and could therefore mean exempt from Rabbinical prohibition (i.e permitted) if absolutetly clear from context.