This is probably the most difficult server to play in Dota 2. It doesn't matter if you're high ranked MMR or playing in a pub-match you will have a taste of what it's gonna be like playing in SEA region.
I have been playing in SEA since I started playing Dota 2. I played in Japan and Australia sometimes, only if the SEA is under some kind of maintenance. Ping wise? it's not that bad, some say it's about 200+ that's an exaggeration. That really depends on the internet connection that you're using. So what makes it cancerous then?
SEA might be the most harshest environment to play in Dota. Racism is always present in every game, even towards those players within the same country. Drafting wise? It sucks, you will have a match where everyone is a carry, which I personally call "dream-team". Sometimes, it is frustrating because you will have cores that will just farm all the way up to 40-50 minutes in the game, when you clearly won the game, is just that your cores doesn't seem to wanna win but want's to have a full slotted items on their inventory. There's also a situation where, everyone is fighting who want's to go on mid-lane, which can be avoided since when you see someone drafted a mid-laner, why would you draft another mid-laner as well? Those who play support, is not exempted. You will have supports who want's to play as carry, sometimes you'll get lucky to have a support player who constantly wards, and seems to know what needs to be done in order for the team to win. Most of the time though, you'll have support heroes who just wanna get a lot of kills, and doesn't care about setting-up kills, warding the map, and most especially buying courier. You'll have game in 20-minutes without any courier, because everyone just doesn't wanna buy the damn chicken. Also, some players who play carry roles, doesn't seem to realize the importance of BKB. And they end up blaming their support/initiator because they died during a clash when he just bursted a lot of magical damage from the opposing team. No communications at all, I understand that there's always that language barrier however, we can always choose the preferred language before you find a match in the game. Racism is everywhere, "Peenoise", "Indogs", "Malayshit", etc... you'll hear this almost every match when the blaming starts. Rage quitters also happens, you'll have this a player when he died 3-4 times in the lane he'll just rage quit with zero f's given. The only time that you'll have a decent game where everyone is trying to cooperate to win, is when you're playing at low-priority match.
All that I just mentioned above, is based on my experience, and it is not changing and I think it's gonna be like this for the rest of the Dota 2 history. What you need to do if you wanna play and win in SEA? Well, my approach is I never ever pick first! Forget what role you're comfortable in paying, make sure that you don't pick a hero right away. At least if 4 of your team mates picked a carry heroes, you still have a chance to pick a support that somehow will manage to help all 4 carries. Mute the damn headset/speaker if you easily triggered from racial slurs or prepare yourself for the greatest insult you'll ever have in your life. Sometimes you will have a decent players, but mostly these are the players who has a 2-3 man parties and they usual cooperate but not all the time. Don't buy items right away, you'll end up not having a courier, so make sure you spare a 100 gold for that chicken. You'll gonna have problems with your map vision, and if you're playing a carry role, just make sure to ward your lane from any incoming ganks at least for you to survive and keep on farming. Don't rely too much on your support, and always check the mini-map for missing heroes in lanes since no one will bother to ping or report it. if you wanna lead the team, do it in a very nice way so that they will obey your commands, if you want to call a gank, gather for smoke, or just as simple as requesting your support to put wards.
Would I blame others for labeling the SEA server as "cancerous"? Probably not, given the things that I have experienced, when you do have a good game, I can promise you that it is the most intense game you'll ever play outside the tournaments. I'll admit though that I might be biased because I haven't really tried playing in other servers like in America, Europe and China but you can't deny the fact that it is really a frustrating server to play in. In the end, I just come to accept that this is the community that I'm part of, and we don't really have anyone to blame aside from ourselves. Would I make a difference in order to change the minds of the people about the SEA community? Of course, however I am just another player and it takes all of the players in SEA to change the community. All I can do right now, is to play the game the best way possible and try not to get really emotional or triggered to the harshest environment known to man.