Suicide—whatever mental/emotional problems induce some to commit it and which might even mitigate its culpability—is objectively a gravely evil action (CCC 2280-2283) and may never be licitly chosen. When committed in a sacred place such as a church or shrine, suicide effects the “violation” of that space and divine worship (as opposed to personal prayers) may not be offered there until the place is rehabilitated in accord with canon and liturgical law (1983 CIC 1211, olim 1917 CIC 1172; see also 1983 CIC 1376).
When Dominique Venner killed himself with a shotgun blast to the head inside Paris’ Notre Dame Cathedral (indeed, it seems, within the sanctuary itself) he desecrated that great church.
If it turns out that Venner killed himself in protest over France’s new “gay marriage” law, then, besides condemning the classical scandal his deed produced, one may further observe that all he really accomplished was to make opponents of “gay marriage” look like kooks, and to deprive, for a time, the faithful of France of a particularly powerful place of worship from which to ask God’s help in preserving the natural and holy institution of marriage in their nation.
Only the Evil One would take pleasure in that.