Even if it could help them, there are risks[0], and in most jurisdictions, LSD is a highly restricted drug which doctors cannot prescribe therapeutically, so there is no guarantee of dose or purity. People with severe depression who would entertain this seriously are already prone to impulsive behavior and cognitive difficulties. The suggestion is irresponsible.
[0] https://medlineplus.gov/ency/patientinstructions/000795.htm
You might as well suggest a sugar pill, then.
There are downsides to LSD. Illegality is probably the biggest. Here's a self-study showing micro-dosing is pointless (for the person) and possibly has harmful trends: https://www.gwern.net/LSD%20microdosing
The reason my advice isn't irresponsible is because microdosing LSD has no downsides. If it doesn't work, nothing breaks. Try something else then.
Depression is a real life-killer, and if 10 people tried my advice, and this worked for only 1 of them (although I think at least 5 would), then this advice has essentially saved 1 life, while not harming the others.