Unfortunately many would-be authors are unable to accept criticism or rejection. Please do not become one of those who resort to abuse, or even death threats, to overcome their disappointment. Shrug your shoulders. Learn from it. This is almost entirely due to the fact that editors are increasingly unable to deal with the thousands of manuscripts that are sent to them each year.
Literary agents act as a buffer for the publishing industry.
If something is submitted via an agent then the editor can be reasonably sure that both it and the author been vetted and are not completely unworkable. Publishers trust agents in a manner they will never trust the general public. I tried for years to have a novel accepted by a publisher. But with BattleAxe I was so determined to give it every possible chance I thought I'd try a literary agent. I love agents.