Yes they are very harmful indeed. Our house had subsidence problems which were found by our insurers to be caused by conifer trees in the next door garden.
It depends on a number of factors; the conifer species, the size of the tree, how close to the house, when was the house built, soil type etc. Large trees, close to a house on shrinkable clay can be a problem as they extract water from the clay causing it to shrink and the house to move with it. If the question relates to direct physical damage i.e. will roots physically penetrate the foundation, then no.