Make it 1,000,000 if you want; they still have to cross a minimum of 12 miles of desert on foot while being pelted with CS gas. Good luck with that. 90% would probably drop out even without the gas. Some of them might have gas masks, but ask those who have used them what it's like to try walking around in a desert while sucking air through a filter. The biggest chalange for the military wouldn't be stopping people; it would be having enough medical aid and water on hand to take care of the civilians passing out in the middle of nowhere.
You might thibk that you could get around those problems if - instead of walking - you had thousands of people show up with trucks and ATVs, and try to drive in as a giant herd. However, in that case, the military would have far better justification for using heavy weapons. A quick pass by an A-10 shredding the lead vehicles would quickly turn the advancing horde into something resembling the Atari symbol.
Any way you slice it, numbers don't help you much; the vast majority of your little invasion will end up running away, and the rest won't be much of a challenge to round up and arrest. The only thing that happens as the size of your crowd goes up is that the likelihood of people getting killed also increases.
