Many people have told me that. But "many" may be a thousand bitcoiners, perhaps, who care for the Core Values; and they may not include any big holders. The other 99% of the bitcoin community (including the Chinese day-traders, who may still be setting the price) probably don't understad why a change in the protocol would be a bad thing, or don't care.
Note that increasing the supply of bitcoins is bad for the price only if the demand remains the same. If there were enough new demand, increasing the supply would not prevent the price from increasing, too.
The traders are not really important for this question, only the miners who are already in competition with each other for a bigger slice of the pie.
Increasing the supply would not prevent the price from increasing but it would prevent the price from increasing *as much*.
As a miner, if you allow the pie to grow, you probably just end up with a smaller slice percentage-wise. Unless you're thinking of such smoke-and-mirrors tricks as moving the decimal place to the right.