In some cases, bitterness means toxicity. Because of this, we humans have evolved to favor sweetness in our food and drink. That is all well and good, but these days most of us have a pretty good understanding of which foods and drinks we can safely consume.
Some people will avoid many wonderful foods just because they have a low to medium level of bitterness. Other people will consume these foods with added sweetener to mask their bitter flavors. In moderation that should be fine, but too much added sweetener may in time contribute to some diseases.
Many healthy foods like tea, grapefruits, and some leafy greens (to name just a few) may have some bitterness, but that certainly does not make them bad. Bitterness is often a sign that the food is high in antioxidants which is a very good thing. I have also read that Chinese and Ayurvedic medicine traditions honor all different flavor profiles and promote the consumption of sweet, salty, sour, astringent, savory and bitter foods and drinks. The key is balance and moderation.
I work in a busy tea house and over the last eight and a half years, I have seen literally thousands of perfectly good cups of well-brewed tea subjected to massive amounts of honey, sugar or artificial sweeteners. I don't want this post to turn into a "bitter rant" (pardon the word play), I only want to suggest that some of us (though probably not many of my readers) are using too much sweetener and thus robbing ourselves of a rewarding natural flavor experience!
I'm not going to lie. I also enjoy sweetened tea from time to time. But I drink over 90% of my tea plain. I sometimes worry about the many customers that I see who are always dumping 3 to 5 (or more) cubes of white sugar cubes into their relatively small mugs of finely-brewed tea. Do they do this all the time or is this just a special treat? Should I ask them about it? Of course not, I should mind my own business.
The Chinese have a saying, "eat bitterness" (吃苦), which is often translated as "the ability to endure hardship." I would like to expand this expression to include its literal meaning as well. Perhaps we should all eat and drink a little more bitterness. If we can't appreciate a food's natural bitterness, then how will we be able to appreciate its natural sweetness?