I’ll give you 3 reasons why I don’t like dubs as a whole in both anime and live action.
1.) During the original production of a movie/series the director is heavily involved in how the character sounds and tailors the voice to what they desire from that character. This doesn’t happen in dubs. A new director is brought in and changes things.
2.) I watch (most) stuff as it airs in Japan and get accustomed to the characters voices.
3.) Dubs often translate things differently from the Japanese translation for no good reason, and I’m saying this as someone who can speak basic Japanese.
4.) I know I said 3 but here’s point number 4. Allot of dubs (and I’m mainly talking about Funimation here) have the exact same voice for multiple characters who are completely different in personality. There’s no change in tone and it skews the personality of the character.
Does the above mean that I don’t ever watch dubs? No. I wouldn’t be able to put forth an argument against dubs if I hadn’t seen/heard them. Dubs are good when you’re drunk and you can’t read subtitles anymore. What annoys me is people who watch dubs assuming that I’m some sort of elitist for watching things how I prefer to watch them.
If you want to watch dubs go ahead, you can eat shit all day as well for all I care, just don’t start preaching to me about how your shit tastes better than my steak.
Anime Tech and Touhou 
Although this post seems to be heavily subjective and something that cannot be rebuked due to this, there are some parts that sounds a bit objective and generalizing, so I’ll touch upon those points.
The part about changing the dub for “no good reason” really cannot be applied to “every” dub. Sure, there are lots of bad examples, like the pokemon “jelly doughnut” lines, but jokes from anime like Panty and Stocking were changed because the word play wouldn’t work in English as it does in Japanese.
The same goes for your fourth point. Anime like Black Lagoon sound better in dub because the varied voice accents fit the stereotypical characters from the series, but the Japanese dub fails in this respect because they mostly have Japanese people trying to speak “engrish” and other languages with only a japanese accent, thus making everyone in the series who have different nationalities seem like they’re from Japan.
Also, please take this as an assessment instead of an offense, but I think some people think of you as “elitists” because of statements like the ones you made in the last paragraph.
I watch mostly subs over English dubs, myself, but I acknowledge that there are some good and bad things in both sides of the competitors.
I admit that some dubs are better than the original Japanese. Black Lagoon is a great example as well as the often mentioned cowboy bebop. As I say to begin with this is more to do with dubs as a whole rather than every dub ever made.