Unless you're extremely wealthy, the fact that you can't participate in investor meetings of stocks you own indirectly through a fund is hardly an issue. Most direct investors have little influence on the actions of the company, because they rarely own enough of the company to make a difference? How often do you hear of shareholder proposals that were opposed by the Board of Directors getting passed? As a practical matter, only the major shareholders have any real control over the company, the rest of us are just along for the ride.
So rather than worrying about your voting ability, think about the flow of money. Institutional investors, such as mutual funds, make up the vast majority of stock ownership (about 75% is in retirement accounts and other tax-free accounts like 529 college savings plans -- see Who Actually Owns the Stock Market). So these funds have a big impact on the companies they choose to invest, or not invest, in.
Of course, your personal choice of mutual fund has about as little impact as your shareholder vote in direct stock ownership. But imagine if lots of other people feel the same way as you do, and all choose socially-conscious funds. That could shift a significant amount of investment capital to those companies, and put pressure on other companies to change their practices.
It's kind of similar to a boycott. A company can easily ignore a few individuals who decide to stop buying their products, but if there's an organized movement it's harder to brush off.
In both cases, you can't really be sure how many other people will act like you do. But you don't have any control over their decisions, only your own. So you act according to your conscience, and hope that there are enough others that it will make a difference. If everyone just gives up because they think their action won't make a difference, it's a self-fulfilling prophecy.