Anecdotal
"dirty":
- When my father was a child, the waste disposal service was so well paid, that it was even attractive to work there for totally overqualified people.
"dangerous":
- coal miners, dangerous good truck drivers,... could works often elsewhere
"difficult":
- that is not a problem at all. Difficulties are challenges and people like challenges

Perhaps there would be problems in Western Europe with home care of old people, which is now often done by eastern Europeans under really bad conditions - and e.g. in Poland similar jobs that are done by Poles in Germany are done by Ukrainians in Poland. OTOH low paid work becomes more attractive with a basic income, and there is the human mind.
When there are problems, solve them. I think the next big technical development will be a much increased use of roboters in everyday live. When some unnice jobs are currently done for very little money, there is little incentive to use capital to improve productivity in such branches. When you can't get cheap labour to do X, there will be an incentive to invest capital, and creativity into doing X better.

Der Amerikaner ist die Orchidee unter den Menschen
Volker Pispers

In an era of mass, structural unemployment, all humane welfare systems end up developing an option not to work yet be bankrolled.

Of course, you can litter those being bankrolled with "back to work" propaganda and useless, time losing "formation", but that is money being spent inefficiently.

And yes, one of the point is to weaken the incentives to work. Debt slavery, workhouses, etc... All great system to push "incentive to work". Still very, very lousy system. And diminishing the incentive to work in low-qualification jobs, which are where, most often, the boss's power is the stronger compared to the worker (see the working conditions in many such jobs, which are, literally, dangerous), is a good thing for bettering the conditions of those who actually do such jobs.

Always funny are the employers in building or restaurants, that keep complaining they can't find workers, yet keep wages low, hours long, conditions dangerous...

Un roi sans divertissement est un homme plein de misères

Sure, but the higher the work-free wage is, the larger the difference between working and not working will be.
I guess you mean lower, not larger. However, that depends totally on the question of how strong additional income is taxes/how strong benefits are reduced, as Bruce pointed out more clearly than I did.

but it have to be linked to forcing people to actively look for jobs.
I don't believe in the wisdom of the gov't. It is very difficult to make a system, which puts pressure on those who don't want to work, and who are willing to exploit every possible trick, without punishing those who are honestly trying to find work.
In the end not too much will change in most western European countries, except the stigma of living a live not focusing on making money.
This can even help to make people doing the things, they are good at, instead of making people do things, somebody invents sometimes only to test the willingness to work, but without practical use.

In the 30s and 40s Gustav Möller was minister, natural resources were cheap and even stupendous work could contribute a lot to the society. Today natural resources are among the core scarcities, stupendous work is often avoidable by machinery, creative actions, that do not immediately produce revenue can be much more worth than stupendous work and the revenues may not be collectible (e.g. open source stuff).
Moreover we are rich enough today, that we can pay enough to survive, but not enough to participate in the general consumerism. Bottom up approaches - such as a market - often do better in being creative and finding well fitting solutions than a top down approachs, that workfare or similar programs will do. In the 30s and 40s coming along was already quite a lot. 750 Euro, a typical students monthly money in Germany, or 9000 Euro/a, is less than 1/3 of the GNP/capita. I doubt that in the 30s and 40s a single could live a rather untroubled live from a third of the GNP/capita.

Der Amerikaner ist die Orchidee unter den Menschen
Volker Pispers

... stealing from the poor?

As a side note, it is in part money that is spent effectively ... it achieves a number of ends, from reducing the disincentives to work caused by unemployment-tested income and means-tested income support, through reducing the inefficiency of European inter-regional transfer payments, to eliminating the fiscal drag from mixed Green/Revenue taxes by converting them into pure Green taxes.

But primarily, if we elect to pretend that it is funded by a neutral tax, then as a system is transfer from the high income to the low income. And since the high income are great net beneficiaries of the common social inheritence of knowledge, technology and established infrastructure, this is not taking, but simply a payment to the Commonwealth for services rendered, distributed as a universal social dividend.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.