That's not an ad hominem attack, it's a statement based on reputation.

Ad hominem, properly, is based on an irrelevant characteristic of the person being attacked. "I won't work for a Peter Thiel startup because he wears white shoes after Labour Day", or "... because he mixes stripes and solids".

Stating that he's got a track record of founding and backing ventures with a net-negative social value, or which simply waste talent, is absolutely spot on.

>founding and backing ventures with a net-negative social value

According to his Wikipage, the major things he's done: Paypal, Facebook, Y Combinator, and a couple investment/VC/Angel ventures. None of these are net-negative social value in my opinion, or at least not any more so than virtually any other big business on the planet. He's also backed an impressive number of philanthropic endeavors.

Your comment comes across as someone's angry at Thiel because of the Gawker lawsuit and/or Trump endorsement.

The factual value of whether or a relevant comparison is justified or not is open to question. That would turn the attack into an unjustified one.

But not ad hom.

I'm not convinced of PayPal and Facebook's net social value. They're quite mixed, though I'll allow transformative.