I wasn't saying we should never voice our opinions. I don't understand why we can't keep stupid shit to ourselves. Things that involve murder, violence, opression, those are the things we DO need to speak out against. But gay rights? Religion? Who gives a shit if John down the street is a practicing pastafarian? Who cares if Laura from accounting is a Lesbian? How does that affect you? Would changing that affect your lifestyle in any way?
For example, slavery. Maybe you don't own any slaves. But if you decided it was wrong, and got it changed, that would affect you by changing the economy. But if you are the deciding factor in creating a law that stops Paul from getting his wife's baby aborted, does that really change your life? Or the other way around. If you are the deciding factor in allowing abortion, does that change other people's lives for the worse somehow?
Back to reason #1: Lots of people believe stupid shit, and their beliefs influence their actions, and their actions affect the lives of other people.
Unfortunately, one of the 'stupid shit' things many people believe is that they should try to change society so to impose their stupid shit beliefs on everyone else. Because they believe this, this influences their actions, and they actually try to follow through and get society changed to enforce their stupid shit on others. This obviously affects the lives of other people.
And, again unfortunately, another thing they often believe (almost without fail) is that their stupid shit beliefs aren't actually stupid nor shitty.
E.g. the vast majority against abortion are that way because they are religious and have a belief in a soul and an afterlife. Lots of stupid shit follows from those beliefs (esp. when combined with the stupid shit in 'holy' books). Saving the imaginary souls of fetuses from an imaginary afterlife of eternal torment is more important to them than actual human suffering in this real world. In fact, some of them think this is the most important thing they can possibly do.
The 'stupid' and 'shit' parts of 'stupid shit beliefs' can get pretty damn stupid and pretty damn shitty. Take 9/11 as a prime example. But it's not just religion. There are lots and lots of stupid shit beliefs around. It's not hard to find countless examples.