There is nothing wrong with single engine IFR, just the same as there is nothing wrong with single engine over water or at night. It is a personal risk assessment choice. Some are prepared to do it others are not, the aircraft does not know it is in cloud or night etc.
There is nothing big and clever about flying along in cloud when the conditions do not require it. You will that us IR pilots try to avoid cloud whenever possible, we plan to get on top and back under in the quickest manner possible. There is way to much macho thinking about flying in cloud. The reason I fly airways everywhere is that with the amount of flying I do the big sky shrinks and in the airways I have a RCS from start to finish.
I fly single pilot single engine IFR all over Europe and have my risk assessment criteria which I am happy with.
I have flown very long legs hand flying in IMC 3 or more hours on occasion and it is very very tiring. I would suggest that it is beyond the experience level of the average IMC pilot to fly by hand for this length of time.
I would also question exactly where the average IMC pilot would actually be flying to be able to stay in solid IMC for this length of time as the rating is illegal to use outside of the UK and the there are few places that you can fly between in the UK to be in IMC for three hours. Doing so would indicate a very poor example of pre-fight planning.
An autopilot in busy airspace is a must to have for a serious IFR pilot. Flying around the LTMA under London Control, getting ATIS, preparing plates and approach briefs is not the place to be wandering off heading/height while you are distracted even for a few seconds. You want to play with the big boys you play by there rules and they do not hand fly.