There is much academic discussion about the concept of raids as they currently are designed in major graphical MMOs. With growing concerns about the addictive nature of MMOs, the fact that raids require 3-4+ hours of constant gameplay leads some to believe they are inherently (and physically) unhealthy.
Also, some game developers believe the way raids and raid guilds can totally dominate your life (dealing with sign ups, planning, guild drama, etc. makes it an almost 365/24/7 commitment) could potentially give people a false sense of accomplishment that impacts their ability to care about real life goals and accomplishments.
Players should be aware of these dangers when deciding if they want to get into raiding or to what extent they want to get into raiding.