Slots at Harvard may be limited but slots at excellent institutions of higher education are not. Seats at ball games are not. Medical residencies are only limited by fiat. That could be fixed if we wanted to. The problem is the artificial limit, not the people getting the limited placements.
What people fail to understand is that immigrants add to both the supply and demand side. An immigrant sitting in a stadium seat is taking a place that could have gone to someone else. But their presence also drives the capacity to build more seats. More demand for higher education results in more capacity for higher education.
Even construction work in Europe is limited. People from Eastern Europe are undercutting German tradespeople and frankly deliver inferior work.
You could hire a German craftsman with the quality of work that was present 30 years ago and the work would last for 30 years. But who is embarking on learning a trade only to be replaced by Poles, Romanians or (in the future) Ukrainians, who will then replace Poles and Romanians once Ukraine is in the EU?
But more importantly, slots at e.g. Harvard are limited. Seats at ball games are limited. Etc. Most things in life are, in fact, limited.
Graham is purposefully misleading here, and he knows it.