There is no "true centrism" regarding the biggest and most important issues because often the choice is between doing something or refusing to do something.
Refusing to do something because one doesn't feel strongly one way or the other is still a choice, and "centrists" think that they're different from the ones who do nothing out of an active choice.
A centrists who chooses "don't pass gun control because I'm not sure it's fair to the market the way it's written, maybe let's revisit and revise" is still choosing a right-wing position. A centrist who chooses "don't pass this immigration reform because it hurts asylum seekers even though it's targeted at criminal offenders" is choosing a left-wing position.
Choosing to not make a choice is still a choice, and again, with large social issues it's unfortunately "with us or against us."