No marketeer would do this intentionally. Avios exist to make us trade up and spend more than we intended. This may be enjoyable. Sometimes it may also be worthwhile but the flight is never truly free.
In short, Avios are not free. Sometimes they are fun and sometines they even give us the excuse we need to spend our own money but they are never truly free.
If, after reading all this you still want to collect miles- go to a head for points. This is UK based and very well researched. The webmaster sometimes sorts out personal problems for people and invites his followers to free drinks paid for by the travel industry. A good guy in a bad field.