I was wondering if polygamy is wrong because a Christan polygamy site states this:
"mia doesn't mean one, it means first in I Timothy 3:2,12; Titus 1:6"
Regarding idios they are saying
"The word "idios" signifies actual or potential corporate possession, or "ownership" (although sometimes the two words may be synonymous, the change up in this verse is very significant). Many times it is used as a corporate simple possessive, like in John 1:11 where John says "He came unto his "own" ("idios), and his "own" ("idios") received him not," or John 16:32, "Behold, the hour cometh, yea, is now come, that ye shall be scattered, every man to his "own" ("idios"), and shall leave me alone: and yet I am not alone, because the Father is with me," or John 19:27, "Then saith he to the disciple, Behold thy mother! And from that hour that disciple took her unto his "own" ("idios") home". The idea is that there were others who were involved with the "ownership". They are "sharing" him!"
Are they wrong with this meaning? Why do so many try to defend polygamy?
The number of people pushing for an idea does not tell whether an idea is right or wrong. It only gives a rough idea of popularity. Frankly, popular ideas are often not good ideas. "Enter by the narrow gate; for wide is the gate and broad is the way that leads to destruction, and there are many who go in by it. Because narrow is the gate and difficult is the way which leads to life, and there are few who find it" (Matthew 7:13-14). What is interesting is that right after the warning on not following the majority simply because they are the majority, there is a section on being careful about false teachers (Matthew 7:15-20). This is because false teachers generally use popularity to push their agendas and because the idea sounds appealing, people forget to ask whether the idea is really true or not.
Regarding the definition of mia, here is what a real dictionary says: "one, alone, one and the same, only one, someone, anyone" [The Complete Biblical Library]. It is used in "There is one body and one Spirit, just as you were called in one hope of your calling; one Lord, one faith, one baptism; one God and Father of all, who is above all, and through all, and in you all" (Ephesian 4:4-6). Each "one" means numerically one and not the first of a set. I looked at all the verses where mia is used and it is never translated as first. Therefore, "Let deacons be the husbands of one wife, ruling their children and their own houses well" (I Timothy 3:12) means a single wife.
The word "own" translates the Greek word idion. It is in the plural form because the subject of the sentence, "deacons," is in the plural. It is not saying that each deacon has multiple homes but the deacons all have homes.
In John 1:11, the Greek word is idia, which is in the nominative/accusative, plural, and neuter form. It means, that while there is a single owner, what is being owned is many. "He came to His own, and His own did not receive Him" (John 1:11). It can't be compared to I Timothy 3:12 because it is in a different form. John 16:32 and John 19:27 are the same form. Basically, the argument is the same as saying that since "birds" means more than one creature, then "bird" also means more than one.
Basically, the people you are referencing don't know grammar and because of that make foolish arguments.