Let's take restaurants as an example:
Take (1)"Ye Olde Club-Membership 5-Star Restaurant", (2)Typical High Price Restaurant, a place like (3)Olive Garden, and (4)McDonald's (but let's make McDonald's only dine IN, no drive thru)...
1- Has a very small group of people, but all act maturely, they do their best to not break rules, etc, the staff operating the place do their best to provide real quality service
*Elite Membership, entry fee, cost of meals plus extra fees, and known for discrimination (If cost of game was 100+ and had 30+ monthly)
2- Has a larger group of people, most act maturely but you get some snooty a-holes that act up, the staff still does its best
*Entry fee sometimes, high cost of food (60 for game, 15 a month)
3- Let's anyone in, mediocre cost of food, some customers are rude to each other and get away with it, staff is like, "Whatever" most of the time, some good ones though
*No entry fees, mediocre cost of food (Free Download and 15 a month, OR 60 for game and 5-10 per month)
4- Anyone gets to eat, crappy food, customers range from people who work to utterly rude teenagers, ghetto crowd plus redneck bumpkins that may even be doing some chaw at the table and spitting in an empty McDonald's cup... and staff doesn't care, they are probably in the back talking on cell phones and getting annoyed that you want to order some time in this century.
*no entry fees, LOW cost of food (30-60 for game, 0 per month)
The difference is, YES you get more people, but of what quality, and will you drive away the people you built the game FOR in the first place? Do we really want 50-100 Dunmer Dual Wielders named various forms of Drizzt running around? What about Breton Sorcerers with grey/white hair + beard named Gandolff, Gondalf, Gahndelf, Dumblydore, Dombldorr, etc? Do we want people joining our groups and looting every chest before we even finish fighting, and then when you complain their response is, "Whatever, you guys svck anyway" and knowing there are 5 million people playing, so this one guy's reputation will NEVER actually get to him and he will still be playing when you get to 50? There are a lot of bad types that ruin games, be careful you do not open the game up TOO much...