With all the work that goes into osu!, people can spare an extra dollar to help keep such a great game running. I see no issues with it.
As for those saying to just "advertise" supporter more, I personally think that would only push people away. Nobody likes having "give me money now" buttons thrown at their face all the time. Everybody already knows supporting is a thing, it's easy to find and easy to do.
In terms of "revenue", the dollar increase isn't going to push people away unless they're real penny pinching cheapskates. And that's coming from someone who's a cheapskate as it is. Being someone who bought 2 years of a supporter just for the cheapest option in the long run (even though I could have settled with 1 year for the same long run outcome).
There was also something said about "infinite amount of supporter tags". While that may be true, there's only a finite amount of players, and those finite amount of players will likely wait until their supporter runs out before renewing it. So even with an "infinite" amount of supporter tags, players aren't going to support an "infinite" amount of times.
Even if some people stop supporting over a dollar, the quantity of supporters who continue to support with paying that extra dollar will still add up to a lot in the end to meet the costs needed to keep everything running smoothly.