Almost all motorcyclists are irrationally opinionated. I know I am, although the only brand that I am prone to put down, my opinion is more related to the type of machine, which is definitely not my cuppa tea, than their ability to make motorcycles.
I find for example the general condemnation of Chinese machines to be irrational given my own ownership of a Chinese bike for which I can find nothing but praise, and the similar experience of several friends. That's bearing in mind of course their price, and while realistically of course they may not be of quite the same quality as the 'mainstream' manufacturers their value definitely exceeds the cheap price in my opinion.
More irrational opinion:- I read on the forum a while back some advice given to someone who was asking about buying a Suzuki DR650. He was advised to shun it because they have an 'exploding' engine! An opinion no doubt based upon a single observation of a machine that may well have been abused or poorly maintained.
Contrast that with the testimonial of LeCap and a myriad of other owners.
For my sins I own a BMW 1150 GS (Oh, shudder!) One of my good riding buddies, otherwise a very nice and generally knowledgeable chap, just cannot resist any opportunity to decry the unreliability of all BMW's. The large final drive bearing for example 'always' fails within 20,000km. This remark was prompted when another friend had to replace his at around 100,000, and the fact that mine shows no sign of a problem at 114,000, plus numerous others that can boast of much higher figures, these are all 'exceptions'. In general they all pack up at around 20k. because someone who does a lot of them told him so.
Same when my fuel pump recently gave notice. I say gave notice because it didn't just pack up and leave me stranded, but gave audible advance warning. Once again my 13 year old unit had to be the exception, because he 'knows' that they all give out at the same ubiquitous 20,000.
As to KTM as a brand I can't comment from experience, but it stands to reason that when a manufacturer boasts that their engine is the lightest and most compact in it's class whilst delivering the highest power in it's class, then more maintenance and shorter component life is probably to be expected, but this is not the same thing as unreliability.
Everyone's experience will be different. for every horror story there will be many contrasting good reports, and I feel that all opinions, even qualified knowledgeable ones need to be carefully considered and seasoned with the proverbial pinch.