That little phrase has been the spark for numerous arguments in the various guilds I've been a part of in my eight years of playing WoW.
Inevitably, it's uttered on the heels of a night of working on a progression boss. A night that has ended up in repair bills. Or even one with a boss kill on the last attempt of the night. It is tossed about with mentions of how raiding used to be fun. And people are taking things too seriously. And how could you have shushed me in the middle of that attempt when I was telling that funny story about what I did over the weekend?
But here's the cold hard truth: the raid boss doesn't care that you're "not a raiding guild." If you and your team want to be taking down new content, at level, while it's still the top-of-the-line tier of instance, you are going to have to take it seriously.
You WILL do better if you have a static team instead of switching players in and out each raid night. Players WILL have to use consumables and ensure they keep themselves gemmed and enchanted to the best items available to them. And your raid leader WILL need to decide upon and coach the team through a winning strategy.
Otherwise, you'll keep hitting your head against the same boss over and over without making progress.
If you want to faceroll content while doing tequila shots, set up a retro raiding night and hit up content from expansions past. Retro raids are a great opportunity to casually play while getting to know guildies and garnering a last few sought after achievements. But it's unrealistic to expect to have a voice chat free-for-all chat fest while taking down new to you content. It takes time and dedication to make progress. And that's not a bad thing.
And that's my 2 copper.