The dissolution of a material thing means that its being as a whole is turned into pieces.
In front of the dissolution of a thing we say that it was that thing and that it does not exist further more, even if we have all those parts that constituted it as a whole.
And thus the lost thing is regretted.
There is not the same case with the dissolution of human ideals.
For the pieces resulted after they are broken down hold untouched the ingredients that makes them to be ideals. It is destroyed the concrete realization of ideals, but not the human resolutions, expectations, desires for achieving them. Human feelings concerning an ideal are preserved through their contribution to the personality of the followers of ideals.
The only effect of dissolution of an ideal is that all of those human feelings are revealed as disparate pieces. Since those pieces are related to a lost whole, someone may laugh at them, as it happens whenever one small thing tries to imitate a big one. It would be a contrary attitude to that of regretting lost things.
Usually, the unhappy dreamer does not laugh, but not because of his lost ideal. He is sad because when he has followed his ideal as a whole, he was building himself as a whole according to that ideal.