A pension is deferred wages; it is not a freebee or a gift, as some people (who haven't had the foresight to work for one) imagine. In normal cirmumstances, the union agrees with the employer that part of the money paid to the worker is transfered to a pension fund, and the employer usually matches that amount. It is a deal negociated in collective agreements, or labour contracts. A pension fund is never the property of the employer since the empolyee contributes to it directly, and is subject to government regulation.
In the case of government pensions though, at one point the government (the employer), grabs the cash and promises to guarantee pension payouts regardless in the future.
So you can't blame the worker for wanting to maintain deals between labour and employer, that were made in the past.
Just complaining that retirees don't deserve their pensions, that the government "can't" afford generous pensions (especially coming from the people who don't have one and are jealous) and they sould be cut and even eliminated, is a bad precedent since it supports the notion that governments can't honour deals they made in the past. It means that any contract you sign with the government is not worth the paper it's printed on should the government change its mind due to popular pressure.
A deal is a deal, collective agreements included, and these contracts should be respected.