tis always a tricky one to do...??
if you come across someone who drops the "techno is mindless" line then it is difficult to explain to them without getting on a soap-box a little bit. these people take many times to have it explained to them OR actually go to a party to find out first hand.
if it is to a room full of punters who expect a certain genre of music that is familiar then it is wise to test them by dropping an unknown or unusual track occaisionally and gauge reactions. track selection here is important as it will be recieved better if the NEW track sits in the mix more fluidly rather than dropped (un-announced so to speak).
don't forget that there is always a percentage of the crowd that haven't heard much at all and certainly don't know tracks as well as a DJ does. they just want a certain "feel" of sound that suits the environment of the club.
there is always a percentage that are the train-spotters or chin-strokers who will always comment about your selection - pays not to listen to them too much as they are generally over it all when they have to start to criticize everything.
a commercial crowd are also fussy and generally want anything that is progressive (ie: beige). if it sounds even remotely energetic or busy they will leave the floor. you tend to just play radio edits to them.
ON THE OTHER HAND....Try playing a live set at a party and you'll soon realise how easy it is to be a DJ and avoid total disconnection of a dance-floor......playing live is the most horrendous experience most of the time. sick of having people come up and request tracks etc. A live set is always experimental and fresh and often just gets everyone in the room staring at you or going to the bar.??