You can put whatever you want in a 401k.
My portfolio is overweighted toward shares of employer as well - it's a form of compensation.
The remedy for this is to sell shares as they vest in order to diversify.
If people had their life savings in the stock these means one of two things: they failed to diversify by selling shares of stock that had vested or they took savings they already had and deliberately overweighted their portfolio toward Enron stock.
Neither was wise.
They could not control what their employer put in their 401k. Enron only put in Enron stock for the employer contribution. Employees were not allowed to sell any those shares until the age of 50. Even if they left the company.
So I repeat. They had no choice with a substantial part of what was in the 401k.
That is one lousy thing to do to your employees, to prevent them from diversifying the employer contributed portion of their 401k.