MRA's are alliances that recruit everyone and anyone. MRA founders do not check for any experience. Additionally, founders of MRA's don't stop inviting, they spend most of their time recruiting. The alliance has to have a hundred players or more to be a MRA.
although there are 100+ player alliances that aren't exactly MRA
MRA started as meaning an alliance that invited a lot of people. That means there could be 200 players in the alliance, and they were the top 200 players in the world. They could still be respected.
But, MRA has evolved to mean an alliance that is mainly inactive and recruits as many players as possible, regardless of their points, experience, or activity.
MRAs can be OK at the beginning as long as you have a lot of time to explain what you want from them and that if they don't keep up, they will be kicked.
But, if you just keep inviting players and don't stop that is a bad thing. Players will just see more players joining the alliance and no thought being given to the players already in the alliance. That lowers moral, keeps players from bonding and forming a close knit group, and doesn't push them to be active and do their best. The good players will leave for a more elite alliance, and the bad players will become inactive, so that the entire alliance will just be inactive dead weight getting rimmed as you try to invite new players that will get rimmed just as soon.