Perhaps. However, we do a similar thing with telephone numbers--to reach most professionals I have to go through a receptionist. The added friction to contact has to be weighed against safety and susceptibility to disruption.
At the very least, a single point of entry to ProPublica's journalists is something the organization can control. It is by scales of magnitude more difficult and intrusive to control spam in the wild.
"Too" intrusive is a question of expediency. In other words, the cost to harassment is low because the price to contact has been set low. Raise the barrier to entry. It will make legitimate contact SLIGHTLY more difficult, but it would also make opportunistic harassment in bulk MUCH more difficult.
