is riding a bike faster is good or bad

Well, I guess it depends on why you are riding the bike in the first place. If you simply use it as a mode of transportation then it would be a matter of good judgement; always keeping your safety and that of others in mind. If you are riding for health reasons, then yes, fast is good, but not necessarily speed fast. It's how fast your legs work, that gets your heartbeat going and is a great cariovascular workout.

Speed of bike isn't that important. But the way you control is more important. If you overtake a 4 wheeler trying hard again to get back on track . You would some day or other land in trouble. If there aren't any curves approaching or 4 roads and you drive at 80,its alright but if you overtake without using you senses and turn sharply ,its certainly not good for you. Let me tell you in short ' car has a spare wheel but we have nothing in spare'

of course you can lol- it's the same with me though i'm not driving with 80 km/h

I think riding a bike at 80kmpr always is not good. Of course u can when it is essential. But at this speed u cannot control it if somebody cross unexpectedly.