How many innocents does he kill

Couple things.

A. Im pretty sure he was only wounding the cops and law enforcement types that weren't directly connected to the scams.
B. When the President of the US is a major player in scamming americans out of billions a year and ruining an untold number of lives, then wielding the power of the US govt to hide those actions, anything you do law enforcement suddenly becomes much more morally justified. (and before some asshole pops in here claiming that the US is already doing that in reality, keep in mind it wasn't some vague conspiracy theory within the context of this movie. It's explicitly shown that those in power were incredibly corrupt.)

You're basically complaining that when Luke blew up the death Star, he killed lots of innocent empire soldiers who were only there to serve the galaxy and be good citizens!

It wasn't just law enforcement, like immediately after he asked that guy for his car keys at the gas station and he drives off, it blows up lol. There were people there filling up on gas.

Jason Statham - 'nuff said (I haven't seen it)

I think the cops he killed at Nine star united building all are mercenaries, and thus Clay considers them goons.
This is what capt Pettis (the leader) said when he introduced his team to the FBI squad: "Private security here on the orders of the Governor." and "Because Mr. Westwyld hired me".

At the mansions, Clay didn't kill any secret service (he shot at their body armor). He only deliberately killed the goons (mercenaries/other beekeepers?) . Perhaps some agents were wounded, like shot at the limbs, broken bones, or explosion concussion, but I believe no agents died.

For the poor guy at the gas station, I think when he gave his car key to Clay drove away should give enough time for him to walk away before the explosion

I have that same problem with this movie and all those like it.
Why is that okay?

What would Adam Clay give as his excuse?

Its kind of slightly amusing, reading folks attempting to 'justify' the collateral damage. But then, we've gotten used to that.

Let's face it - this is nothing but yet another orgy of violence wrapped in a thin veneer of righteous indignation. The nagging reality that our global 'network' is infested with parasitical fraudsters that we'd all, and I do mean pretty much all, like to see hang by piano wire.

This is about the most ham-handed wish fulfillment vendetta vehicle imaginable. Literally a comic book.