In the most basic way, a conspiracy is a secret agreement or one that is not transparent to a general public that involves something the conspirators plan to do to create a change in a group of people, in the environment, in society or in the world.
That said...in a low-key way, you have to admit that TONS of conspiracies are in the works all the time, all over the world...and many "conspiracies" have nothing to do with anything harmful.
Popular Culture takes the definition of "conspiracy" further and generally, makes a definition that most people are familiar with and that most people hold to - whereby "conspiracy" means something very definitely bad and harmful.
By contrast, the planning of a surprise birthday party is, technically (on a very low-scale), a conspiracy - and one to which few people will object or find harmful. If you've helped plan a surprise birthday party for someone, you're a conspirator! I'm sure, of course, that you intended no harm whatsoever for the birthday boy or girl or upon any of the guests of the birthday party - but you probably involved yourself in meetings that were kept secret from at least one person, would influence that person's (or several peoples') time, mood, schedule and life - for at least a significant several hours of a particular day. You created a change in environment, mood, possibly a significant impact upon a relationship or several relationships between you, the "uninformed" person(s) and people you conspired to bring to the surprise birthday party event. Congratulations, CONSPIRATOR!
Most dictionary definitions of "conspiracy" do, in fact, mention conspiracy is something covert, secret, harmful, and illegal however, the Oxford dictionary also puts forth an alternative definition more in line with what I'm suggesting about conspiracies and an overlooked definition of "conspiracy" that I tend to remind people about all the time - as I am doing in this post...
The Oxford alternative or secondary explanation for "conspiracy" is: the action of plotting or conspiring.
Now, although I've given the surprise birthday party suggestion above, I don't mean to present that I never think of "conspiracy" in the pop-culture way...because I happen to think that most conspiracy or conspiracy theories worthy of discussion are discussed out of concern for ethics, fairness, fear of harm upon individuals, targeted groups and society, in general.
It just helps me to start with the basics of what conspiracy means...so that I don't automatically tip over into a non-objective manner of thinking when I first hear the word "conspiracy." I tend to automatically jump to the pop-culture way of thinking and start looking for groups, individuals and entities to blame for problems and such if I don't remind myself of what "conspiracy" means at its basic level.
Public reaction to the words "conspiracy" and "conspiracy theory" seems to be derogatory - and when people shy away from conspiracy topics because they are convinced that conspiracies and conspiracy theories are distasteful, the public also veers right away from most of the issues that may be involved within a perceived conspiracy or conspiracy theory.
Hopefully, in future discussions, people will be able to differentiate between pop-culture and common thinking about certain terms versus applicable meaning of words and terms - so that important matters related to conspiracy and conspiracy theory can be discussed here, misunderstandings can be avoided, and unnecessary judgments can be cleared away, leaving topics open for discussion and participants feeling they'll be safe to speak/write freely.