When I first started getting into producing electronic music, I was told one thing as being fact: you SHOULD NOT use synth presets. Using preset synth sounds and the drums that came with your DAW was talked about as if it was an unforgivable crime. But this is all completely wrong. If you find the sound you want in a synth's preset bank, use it! Sometimes the presets will contain exactly what you need for your track. Same goes for loops. If a loop fits perfectly in your music and fits your artistic intent, feel free! There's no reason not to.
However, I don't condone laziness. If you have a perfect sound in mind and have the ability and knowledge to create it but then just use a loop instead, I see that as being lazy. So is making a "new track" simply by arranging old loops.
And a final thought - Think of some of the great composers of the past, well known for creating some of the most important and influential music in the world. What were they composing for? An ensemble like an orchestra, which is a set of completely pre-defined instruments.