Where did you hear carbs are bad.
It's not that they are bad necessarily, but we eat them at levels which aren't optimal, even those of us who are not obese.
Generally, this kind of goes along with the keto fads, there are researchers from that community that bring up pretty salient points. However, with any of this kind of stuff there are logical points to both sides.
The basic premise of my point is that we as a culture consume far in excess the required amount of carbs our bodies need per day. Individuals who frequently use anaerobic movements (athletes generally), of course need to supplement the extra carbs, but the layperson shouldn't need to go that far. Most glucose requirements, if needed, can be synthesized into glucose from protein, or simply use ketone bodies.
So where physical performance isn't a factor, it seems like the risks (inflammation, normal flora adulteration, cancers, effects of neurological disease, dopamine fluctuations/mood destabilization..++) of excessive carb consumption outweigh its benefits (dopamine).
I won't go so far as to say a lower-carb diet is what everyone should aspire to, however eating excessive carbs makes about as much sense as filling your gas tank so much it spills onto the ground.
What are your thoughts on heart disease and diabetes with regards to nutrition.
Generally, I think a lot of contemporary nutrition science is dated, as least as far as what is known/accepted in the public.
Heart diseases has far too many causes to 100% secure prevention. Diabetes is a tricky one for sure. Mainstream medicine has people believing people will die if you can't consume sugar. However, ketogenic diets (medium intake of protein, high in take of fats, no sugar/complex carbs) are becoming increasingly popular to treat Type 1 diabetes among those dedicated enough to make it a lifestyle, as well as show efficiency in helping people lose weight ( Which may help those trying to put Type 2 into remission.). Evidence of that will vary dependent on the individuals undergoing the diet as well as variables like exercise etc.
Eat within context of your activity level, avoid foods that send your brain into chemical spirals. Mainly avoid habitual use of sugar, it's as close as you can get to crack cocaine in the food world. And your body treats it like a drug.
(Good) Fats are significantly more important than most people give them credit for, as they help synthesize hormones and hormones regulate your body. If you wonder why old celebrities look so damn young sometimes, many of them take hormones. (They made trade years off their life for this.)
Protein for muscle/tissue/cell synthesis etc.
Sugars, for athletic/mental exercises activity that requires short term high performance. Meaning, eat to fill your glycogen reserves and/or to use during the activity.
Vitamins/electrolytes/minerals are important for normal function.
You're not gonna prevent everything, however you can decrease the likelihood you'll be affected by some disease. Body/mental health can be cumulative and often weird stuff affects that as well. Also, should your body be running in order, then treating yourself to unhealthy things will make less of an impact than otherwise.
If you're trying to increase your life span, Some of the smartest people in the world barely eat anything and subsist on pills mostly afaik. There is a famous inventor like that. He's waiting for the singularity. Still intermittent fasting has it's benefits as well.