saying whatever one wants; unrestrained complaining
Typically used in negative contexts where someone vents complaints, insults, or harsh words without restraint. Often appears in phrases like 言いたい放題言う.
He said whatever he wanted at the meeting and made everyone uncomfortable.
Because it's anonymous online, there are many comments that say whatever they want.
Means 'doing as one pleases' in general, not limited to speech.
Compound of 言いたい (want to say) + 放題 (as much as one likes). The expression literally means 'as much as one wants to say'.