My opinions are formed by witnessing friends getting fired/being pressured to quit because their company had run out of money, or because they had to take care of an ill relative and the company felt that their performance wasn't as good as what it used to be, or because of some BS office politics. Those companies include small trendy startups and big fortune 500 companies alike.
At the end of the day, no matter how wonderful everything is, if the company is having a hard time and they need to fire you, they'll do it. Your boss is not going to sell his car or house to pay your salary.
If the company is doing well and offers a nice work environment, it can be fantastic, as you described- in which case, enjoy the ride while it lasts. But don't delude yourself in thinking that the wind won't turn if bad times hit. Believing anything else is setting yourself up for major letdown when it happens.