Many people are doing that now, because mining for Dogecoin has been going on for a long time, as I remember there are several sites that provide Dogecoin mining, but I think that as long as mining does not involve capital it will not be a problem, unlike investment, because this must start with some considerations Moreover, the condition of Dogecoin is not in the big hype it used to be, but in the short term, as long as it can make a small profit, it's not a problem.
Free mining can sometimes also be a scam in the end so this should also be considered very well by those who want to use their time for mining, because there is no guarantee on any site to keep getting paid when it has been mined for a long time, so mining is not forever free it can pay everyone now.
I don't really understand the problem of mining from free sites, but in 2017 I've done it several times, the results are in the good category and not a scam, after that I never do it again, because my focus has been on the bounty, indeed there are some friends who say that mining on some sites is usually a scam, but because at that time I wanted to try it I continued to do it, and today I have not heard of the mining anymore