Red bell peppers are actually quite sweet. Green bell peppers aren't really bitter, they're just bland, and unripe. The order of bell pepper ripeness is green, yellow, orange, then red.
Taste is each individual business. Annoyingly both sides have a propagnda infection. Haters or simply people who dislike it has a need to spread their hate about it. Due to economic reasons won't waste on stuff with bad reviews. Others, those who enjoy it, will insult haters and blame them for fail.
You could make a passable bellpepper cupcake the problem is that it would still be a lose lose situation. It doesn’t taste like bellpepper anymore so bellpepper fanatics will be upset. It is not as tasty as regular cupcakes so cupcake lovers wouldn’t like it either and would be more expensive.