It's okay for you to not care about them.
But, don't be surprised when they don't care about you.
First, you must learn that centrists and independents are two different things. Independent is an even bigger tent than the D party, it includes centrists within, but includes everybody else, too, like socialists. They're not centrists, don't be ridiculous.
Next, you must learn that If you don't serve the interests of that 40% of voters, you will lose. Their priority one interest is one that we all share, all 100% of us have this exact same interest. Money. We all need money in the USA. It's our common denominator.
You're outnumbered and doing the rookie thing, and gotta up those numbers. Hostility is not your friend. Be honest... if you want to sell something, you don't insult the buyer, do you? You don't have to sugarcoat or lick their boots or anything.
Do the math. If the 40% of independents were centrists or red voters, you'd never win any election, ever. But you do win elections, because they're not centrists or red voters. Come on now