Capitalism per se is not evil, but there is a mindset of many capitalists that is indeed in conflict with Christianity. It's when you view money as an end in itself instead of as an instrument. Pursuing money for itself is a form of the sin of greed, one of the seven deadly sins. And doing so also can easily abet the sin of pride. Relying on money for your security instead of on God is also a sin. Being very careful about your money instead of spending it in love without such care, is a sins as well, as we are called to love without limit.
Not for nothing did Jesus declare it is harder for a rich person to enter heaven than for a camel (or rope) to go through the eye of a needle. Not for nothing did Jesus often advise rich people who wanted to follow him to donate all their wealth to the poor.
Some here have pointed out how capitalism has led more people out of poverty, as though that were a good thing, and as some kind of justification for the evils associated with capitalism. But this is mistaken thinking, because Christian ethics is not utilitarian; we are called to give up sin entirely, rather than justify some sins because they reduce other sins. And given how often Jesus advised people to enter poverty instead of escape it, it is not clear that enabling people to escape poverty is really a good thing as some claim.
In short, it is not at all easy to pursue a capitalist career and practice Christianity.