I posted a pic of D.D. God Dragon FTK'ing, in a ygo group I'm in and was asked if they were real. i told the guy, then another guy comes out of nowhere and this is how a portion of the convo went:

Lane R - I hate god card decks damn creator god of light and banishing the three god cards the return from the different dimension

Andre W - lol even IRL, with my Oricas, i'll ask my opponent if they want me to take D.D. God Dragon out during the duel. This deck is a beast either way though

Lane R - note though its d.d god dragon might not be a real card only fan made

Andre W - are you telling me or anyone else that might be reading?

Lane R - you cause i don't believe they made a D.D. god dragon

Andre W - <<<<<< I made the D.D. Dragons archetype (blah, blah, blah...)

Lane R - oh i don't duel those who use fake cards so maybe that's why i never heard of them

Anyone esle get these? There's like an arrogance with people when they hear about out of game cards. I thought, as duelists or just gamers in general, that we're supposed to be hyped to take on new, unknown challenges. I felt like Goku sensing a stronger opponent when I saw the decklists for the Orichalcos Challenge. That was exciting, even though it was OP, because the OPness itself is the challenge. These people will netdeck like crazy though, but don't like fake cards. I had that argument with my ex fiance. I asked, "What's the difference between my cards and ones already out in Japan that aren't released here? Or ones you just don't know are out there?

the amount of times i got beaten by Six Samurai and got called noob by opponent at the same time is really high. Then i started running an anti-meta deck and got called noob more for doing that, because everybody was playing Six Samurai at that time and Skill Drain just shut them down

It's messed up when people take the fun out of a 'game', especially when the creator has made such efforts towards positive player interactions.

The biggest issue with dueling against custom cards is that they are not real, obviously. A lot of people are playing the game to see how good their build is, and going against custom archetypes does not help them to figure out that they have one of the shittiest Mermail Decks possible, while going against a Deck that actually has a reputation in the game (such as Fire Fists, Vampires, or even Lycanthrope.dek just for the lolz) could help them to realize the Deck's power. They expected to go against something real, but their duel against a "Potato Samurai" Deck doesn't help them to decide if Papi is still a good card this format. When you're dueling with custom cards, only the custom card user will be learning from the experience, since the opponent has no idea whether the "Potato Samurai" archetype is tier 1, tier god, or weaker than Arcana Forces. Nor would they know if the archetype has a good matchup against their Gogogo Zombie build or not.

It really helps to have the opponent know beforehand that they will be facing off against a custom card Deck. This is where DP really shines, since that site is designed explicitly for the use of custom cards to be pitted against one another. There are hardly ever any "real card Decks," so you won't run into the sorts that want to test their Dragon Ruler Sidedeck options against the meta. Of course, this is a disadvantage in itself since there are not really any established power levels, but meh.

Oh, and this is a completely different topic in and of itself, but netdecking isn't as evil as you believe it to be. There are many players out there who do not truly know how to optimize their Deck to the fullest potential (myself included), and taking the best Decks for an archetype is what helps them to learn the game at expert levels. It takes out a lot of experimenting that would only drag out the time it would take to make the Deck as optimal as possible, since you really don't need to waste your time wondering if Indomitable Fighter Lei Lei would be all that useful in Fire Fists prior to having the build perfected, since the difference between good and bad builds modifies how good the cards work in said Deck.

I personally think that the process of finding out that Indomitable Fighter Lei Lei is bad in Fire Fists is actually one of the fun parts in yugioh: the learning process. Anyway, if you netdeck without actually learning, you're going to suck badly at first. The way the duelist like to play (aggro, stun, etc.) also matters; e.g. it was through netdecking that I found out that I didn't like to use the Prophecy archetype. 

Oh, and about custom cards, if you played Duel Monsters on BYOND, you could use anime/manga and custom cards, which only added to the yugioh experience; there was no difference between using a card that was real, a card that was anime or manga, or a card that someone made. The main difference between players who played these games on BYOND and the people who play DN/YGOPro (especially YGOPro) is that the BYOND players didn't care that much about the real life card game, since they were playing a game which had a pace of its own.