Why do some people insist on calling it "profit taking" when they convert Bitcoin to fiat currencies like dollars or euros?

What they're really doing is giving up their hard-earned Bitcoin by gambling it on fiat currencies.

There's nothing wrong with spending Bitcoin on things that improve the quality of your life as long as you realize you're frittering your Bitcoin away. If you can get the things you really want without seriously cutting into your Bitcoin profits, go for it. Life's too short.