>>And I know that there are scientists that spend time doing research that would prove them wrong, but a large part of the scientific society still assumes them to be correct.<<
Until they are proved wrong what else would you like people to do with those theories? They work. They have stood up to every test so far conceived to check them and they work. It is not therefore an assumption that they are correct or useful.
>>How one could make such an assumption as light being the cosmological speed limit, I find most boggling.<<
He didn't make that assumption, he applied the scientific method and tested it, then concluded that light was the cosmological speed limit. HUGE difference.
>>Yet what could be even more boggling, is how people react to this assumption and believe it based on solely Einstein's credibility as a brilliant physicist.<<
NO. Based on the fact that in the near century since he proposed it not one experiment ever by anyone has proven him wrong. No scientist worth his salt would EVER say 'Einstein says it so it must be true'.
>>What if they weren't correct?<<
Newton's theory on gravity ISN'T correct. That's why Einstein worked on the problem in the first place. Newton works fine for applications here on Earth (and is a lot simpler mathematically, which is why it is still used and taught in schools), but once we get into certain areas things start to break down. A fact that was realised very early on when Newton's laws failed to correctly predict the precession fo Mercury's orbit. Einstein's did correctly match observation, and so they were used in suitable applications.
It is also worth pointing out that Newton's laws of gravitational attraction were used to correctly predict and locate the position of Neptune, a planet unknown up to that point, and only discovered by realising Uranus wasn't where Newton's equations said it should be based on everything known at that time. It was postulated that an unknown planet beyond Uranus was perturbing it, and the caluclations were done to show where this planet should be, and then BINGO, they turned their telescopes on that point and there it was.