I think today it is mostly supposed to work through the individual faith of the excommunicated. The famous Catholic guilt you've heard so much about. Those who are excommunicated are supposed to feel bad that the church is angry at them so they will confess their sins and repent so they can be let back into the church.

If on the other hand you think catholicism is a load of bollocks and only belong to the church by accident of birth there's isn't much the church can do about it. They might deny you sacraments but why would you want those in the first place if you don't believe in it? For the ex-catholic an excommunication can only be a minor nuisance like not being able to get married in Catholic churches or like the more zealous of local practicing catholics thinking you have been very naughty.