Pros
The security industry is very competitive and a low-margin business. The clients are very demanding and unwilling to make an investment in personnel development. For those starting their careers, it's a great place to start and learn. However, as a long-term career it is difficult to move up as there are limited opportunities or the contract may fall to another vendor and you start over again in building your reputation and network.
Cons
The industry in general has a high turnover rate and the caliber of individuals, depending upon the contract, is not consistently high. As a result, there are those who tend to be the chronic malcontents. Granted if they had the ability, they would be in another industry or job. If you chose to be in this industry, be the best you can be and improve upon yourself if you are unhappy.