I was playing as Riven and went top with my 3 allies as per the usual. Lux went bot against a Malzahar. Lux was struggling against Malzahar and nearly lost bot several times, so I preemptively ganked and killed Malzahar multiple times.

A member of my team, noticing that I was helping our bot, told me in a condescending way to "not run this two people bot thing", followed by a "^" from one of my other allies in agreement with him. I was also accused of being a bad teammate by the same person for assisting our struggling bot lane.

I switched with Lux and destroyed Malz, capped his bot multiple times, 19/6, and had the highest score in the game. Throughout the game when Lux (who was grateful for me helping her, I assume) said gj and such when I killed Malz. I said no, I'm doing badly (in a condescending way), because I wanted to get back at the ally who accused me of being a bad teammate. I didn't flaunt my score, but in fact one or two people said in the post-game lobby that "Riven was the only reason we/you won."

Basically I'm curious how you handle people who accuse you of bad decisions/playing poorly when you have to help bot. Because when your bot lane dies and you divert down there to keep your point from being capped, your allies engage in a 3v4 up top and start pointing fingers.

I refuse to believe I am a detriment for briefly helping the bot laner (in the form of a gank or wave hold until they respawn) when they are struggling. There are certain push lanes that almost always require ganks/saves.

Prior to lane switching, when you ganked Malz bot were you capping the bot tower too? If so, nothing wrong with that. However, if they had sufficient time to bring a 2nd person bot and protect the tower from you and Lux and your top team was still failing at windmill, the better move might have been to just suggest a lane switch outright so you had 4 top.

It doesn't sound like you did anything strategically wrong, but its hard to tell given only 1 side of the story. Ganking is effective, but you need to cap that bot lane when you do otherwise its just more time lost trying to recapture top.