Most HOAs are mandatory, largely because not many "homeowners" would want them once they find out what they really are. HOAs provide a springboard for volunteer "boards of directors" - (officials) to take control of a neighborhood.
Fraud in mandatory HOAs is frequently quite prevalent and very difficult to prove, usually because it is almost impossible to obtain copies of the relevant HOA records needed to prove fraud, conflict of interest, and collusion. In the interests of collusion HOA boards are very often aided and advised by HOA management companies, HOA attorneys, and HOA industry trade organizations.
HOA operating procedures are summed up beautifully by this quote from Frederick Douglass, "Find out just what people will quietly submit to, and you have found out the exact measure of injustice and wrong which will be imposed on them, and these will continue until they are resisted with either words or blows. The limits of tyrants are prescribed by the endurance of those whom they oppress."