The fact that Communist regimes have attempted to co-opt May Day is no reason to imitate them in a second co-opting attempt. May Day not only originally was, but still is, primarily a celebration of workerss movements generally, not of the butchers of Kronstadt. The holiday is commemorated all over the world; it is not now and never has been mainly a Communist regime holiday.
I think Shawn in the comments (here and here) hits the nail on the head when he describes the attempt to make International Labor Day about the crimes of governments rather than the struggles of individuals, to turn a workers celebration into a day of mourning, as making a false parallel between popular struggles and state crimes. (See also some of the commentators at Radley Balkos May Day blog post.)
Also: if were going to remember victims of the state on May 1st, surely the Haymarket martyrs have a claim to precedence.
Jacob adds, rightly, that the war on May Day is pointlessly antagonistic toward social democrats; but I would just add to this that its not just social democrats who would be pointlessly antagonised. Free-market libertarians have been part of the labour movement since the beginning, from the individualist anarchists of the 19th century (including Thomas Hodgskin, Benjamin Tucker, Lysander Spooner, Ezra Heywood, Francis Tandy, Dyer Lum, Voltairine de Cleyre, and even to some extent Herbert Spencer, Gustave de Molinari, and Wordsworth Donisthorpe) to the ALL/C4SS crowd today. (C4SS went on strike to commemorate May Day yesterday.)
A day for remembering the victims of state Communism is a fine idea. But, as Jacob reminds us, there is already a Day of Remembrance for Victims of Stalinism and Nazism. Wouldnt it make more sense to fold a remembrance of victims of other communist and fascist regimes into that, rather than trying to imitate the Stalinists by seeking to co-opt May Day?
Workers of the world, unite to defend May Day!