I will just speak for myself;
3e definitely caused me to be a bad DM. I'll just list my points below:
1.
3e caused me to turn to crack. I bought the BoVD and read the chapter on drugs in the game, and that got me hooked. I spend most of my days roaming around outside mumbling things about Pazrael, Graz'zt, & Demogorgon.
2. I yell at my players a lot more. My players learned the rules much better than I did, and I'm supposed to be the DM. They didn't do this in 2e. I was able to make rules up as I went, but now when I make up rules, they correct me and expect me to look at it in the book. I'm here to kill their PCs, I don't have time to look at the rules.
3. I'm a much fatter DM now because of
3e. During 2e, I only had 1, maybe 2 players playing at a time. Now I have 8 players at my table and every one of them brings snacks. I can't stop eating. I was a pretty good looking DM in 2e, now I look like Fat Albert after he swallowed the Kool-Aid man.
4. I'm a pervert now. More chicks started playing after
3e was released. Half of my group is filled with them. I can't stop being inappropriate with my NPCs whenever they are roleplaying (even when they are playing Half-Orc PCs).
5. I constantly break the DMs code by telling
4e DMs that their edition sucks. I used to do that back in 2e, and I'd tell the 1e DMs their edition sucks. But 2e was the newer edition at the time, so it was accepted. But since I don't DM
4e,
I'm called the bad guy for trashing the newer edition!
6. I used to roleplay a lot in 2e. It made it easy because TSR had all kinds of fluff in their books. But the only fluff in my
3e books is at the beginning where it lists who wrote the book & who did the illustrations. So I'm not sure how I'm supposed to roleplay
3e.
7. "Play-styles" "Shmay-styles"...back in 2e, there was only 1 play-style...it was called the "rip their heads off, take their stuff, brag about it in the tavern, then rip the tavern guys heads off & take their stuff cause they disrespected me when I was bullying them" play-style. Now I get new players quitting my games left & right because I have a different "play-style" than they do.
8. I was always a real jerk, even in 2e. A good DM needs to roleplay bad guys well, so I had to become a jerk so I'd be a better roleplayer. But
3e brought about all of these D&D forums where people do nothing but whine about stuff. This caused all of my players to have feelings & they got overly sensitive. So now if I roleplay my bad guys properly, all of my players start tearing up, hugging each other, and complain to me that I'm being mean. So now my bad NPCs are just Gargamel bad...not bad enough to scare my players, but just bad enough to scare a Smurf.
I'm sure there are more reasons why
3e made me a bad DM, but this is all I have for now.