I have no problem with adverts in avast free, but this FUD isn't an advert and will no doubt have the reverse effect than its intent. No purchase of AIS or Premier and more likely the loss of an existing customer.
Whilst they may be free users, the cheapest and best advertising is word of mouth. Yet negative word of mouth doesn't just lose one user, it loses any positive word of mouth and is more likely to be negative word of mouth.
I'm no marketing expert, but this just doesn't appear to make any sense.