Look, if your inability to understand the language is getting in your way, perhaps an unabridged dictionary will help.
If marriage is limited to one partner per person, then legally one can marry no more than one person at a time, so no others are implicated (actually or potentially involved) in that union.
If marriage is not limited to one partner, then legally one can marry others, implicating (potentially involving) more, or many more, than one person in that union.
Monogamous marriages legally affect no other marriages. Polygamous marriages legally could affect all other marriages.
A rational basis to deny marriage to more than one partner at a time is to limit the affect of one marriage on other marriages.
Limit the "affect"!
Speak English dummy! I