פירוש על סנהדרין 48:15

...Mishna: And these are the ones ineligible -- to be judges or witnesses

and these are the ones ineligible -- there is a version of our mishna that adds the word "avadim." Whoever has this version, thinks that our mishna lists people who are disqualified on a rabbinical (d'rabanan) and torah (d'oreita) level. But this is not correct since our mishna deals only with people who are disqualified based on d'rabanan. For example, a thief (gazlan) is not listed since he is pasul d'oreita. (Even though it seems like the things listed are פסולי דאורייתא Tosfot will prove how they are not because the person did not have willful intent to violate the torah.)

one who plays with dice -- All of these people listed are thieves who will become rashas and therefore cannot be witnesses or judges

1) Dice players: Even according to those who consider it asmachta since there is no valid transaction so it is stealing and therefore an איסור דאורייתא, it is not פסול דאורייתא since he does not have the intent to violate a prohibition. And according to those who invalidate it because it is not "ישובו של עולם (contributing to society)", it is certainly only פסול דרבנן.

2) Those who lend on interest: This is speaking about interest that is not fixed and therefore only איסור דרבנן. And even if it was talking about ריבית שקצוצה, this is not איסור because the debtor gives the money of his own free will, in which case the creditor is only פסול מדרבנן.

3) Pigeon racers: These are also פסול מדרבנן since bird flying is racing and therefore gambling, so the same concept of asmachta applies here. And according to those who interpret "מפריחי יונים" as "ארא" (pigeons that are trained to bring back pigeon's from another), this is only forbidden by the rabbis to keep the peace.

4) People who deal with shmitah produce: this only speaks about sheviit nowadays, which is only איסור דרבנן since most people live outside of Israel. And even if the mishna is talking about sheviit d'oreita, it is not considered an איסור since they are helping the poor.